A cryogenic torsion balance using a liquid-cryogen free, ultra-low vibration cryostat.

We describe a liquid-cryogen free cryostat with ultra-low vibration levels, which allows for continuous operation of a torsion balance at cryogenic temperatures. The apparatus uses a commercially available two-stage pulse-tube cooler and passive vibration isolation. The torsion balance exhibits torque noise levels lower than room temperature thermal noise by a factor of about four in the frequency range of 3-10 mHz, limited by residual seismic motion and by radiative heating of the pendulum body. In addition to lowering thermal noise below room-temperature limits, the low-temperature environment enables novel torsion balance experiments. Currently, the maximum duration of a continuous measurement run is limited by accumulation of cryogenic surface contamination on the optical elements inside the cryostat.

A low-frequency torsion pendulum with interferometric readout.

We describe a torsion pendulum with a large mass-quadrupole moment and a resonant frequency of 2.8 mHz, whose angle is measured using a Michelson interferometer. The system achieved noise levels of ∼200prad/Hz between 0.2 and 30 Hz and ∼10prad/Hz above 100 Hz. Such a system can be applied to a broad range of fields from the study of rotational seismic motion and elastogravity signals to gravitational wave observation and tests of gravity.

Constraints on Axionlike Dark Matter with Masses Down to 10

We analyzed a 6.7-yr span of data from a rotating torsion-pendulum containing ≈10^{23} polarized electrons to search for the "wind" arising from ultralight, axionlike dark matter with masses between 10^{-23} and 10^{-18} eV/c^{2}. Over much of this range we set a 95% confidence limit F_{a}/C_{e}>2×10^{15} eV on the axionlike decay constant.

Colorectal premalignancy is associated with consensus molecular subtypes 1 and 2.

Background: Gene expression-based profiling of colorectal cancer (CRC) can be used to identify four molecularly homogeneous consensus molecular subtype (CMS) groups with unique biologic features. However, its applicability to colorectal premalignant lesions remains unknown. Patients and methods: We assembled the largest transcriptomic premalignancy dataset by integrating different public and proprietary cohorts of adenomatous and serrated polyps from sporadic (N = 311) and hereditary (N = 78) patient populations and carried out a comprehensive analysis of carcinogenesis pathways using the CMS random forest (RF) classifier. Results: Overall, transcriptomic subtyping of sporadic and hereditary polyps revealed CMS2 and CMS1 subgroups as the predominant molecular subtypes in premalignancy. Pathway enrichment analysis showed that adenomatous polyps from sporadic or hereditary cases (including Lynch syndrome) displayed a CMS2-like phenotype with WNT and MYC activation, whereas hyperplastic and serrated polyps with CMS1-like phenotype harbored prominent immune activation. Rare adenomas with CMS4-like phenotype showed significant enrichment for stromal signatures along with transforming growth factor-ß activation. There was a strong association of CMS1-like polyps with serrated pathology, right-sided anatomic location and BRAF mutations. Conclusions: Based on our observations made in premalignancy, we propose a model of pathway activation associated with CMS classification in colorectal carcinogenesis. Specifically, while adenomatous polyps are largely CMS2, most hyperplastic and serrated polyps are CMS1 and may transition into other CMS groups during evolution into carcinomas. Our findings shed light on the transcriptional landscape of premalignant colonic polyps and may help guide the development of future biomarkers or preventive treatments for CRC.

A reference-beam autocollimator with nanoradian sensitivity from mHz to kHz and dynamic range of 10(7).

We describe an autocollimating optical angle sensor with a dynamic range of 9 mrad and nrad/√Hz sensitivity at frequencies from 5 mHz to 3 kHz. This work improves the standard multi-slit autocollimator design by adding two optical components, a reference mirror and a condensing lens. This autocollimator makes a differential measurement between a reference mirror and a target mirror, suppressing common-mode noise sources. The condensing lens reduces optical aberrations, increases intensity, and improves image quality. To further improve the stability of the device at low frequencies the body of the autocollimator is designed to reduce temperature variations and their effects. A new data processing technique was developed in order to suppress the effects of imperfections in the CCD.

[Twenty-five statements on early initiation of fixed combination ICS/LABA treatment for asthma and COPD in primary and secondary care: consensus research by a modified Delphi process].

BACKGROUND: Guidelines recommend the addition of a long-acting ß2-agonist (LABA) for patients whose asthma is uncontrolled on inhaled corticosteroid (ICS) monotherapy. For COPD patients the addition of an ICS to a long-acting bronchodilator is recommended for symptomatic patients at high risk of exacerbations. We examined whether in real-life practice guideline recommendations may delay optimal timing for initiation of combination treatment. METHODS: A modified Delphi process was undertaken with a panel of physicians, including six GPs and four pulmonologists, in practice in Germany. The first round comprised a semi-structured questionnaire, the second stage was an online discussion to reach consensus on 25 statements concerning the use of ICS/LABA in patients with asthma or COPD. RESULTS: Consensus was achieved on 24 of 25 prepared statements for early initiation of fixed ICS/LABA combination treatment. The panel agreed that a meaningful share of their asthma patients on ICS monotherapy experienced symptoms and exacerbations that should lead to addition of LABAs and that timely initiation of ICS/LABA therapy in asthma patients could improve asthma control, and prevent a significant number of emergency room visits, hospitalisations or additional specialist visits. The panel agreed that symptomatic patients with moderate to severe COPD, and frequent exacerbations should receive ICS without any delay in addition to their bronchodilator maintenance therapy. These patients could benefit from fewer exacerbations and a reduction in symptoms. The panel reached a consensus that fixed-dose ICS/LABA could have a positive effect on adherence, compared with separate inhalers for ICS and LABA, which may impact treatment outcomes. CONCLUSION: A panel of ten physicians working in primary and secondary care agreed on 24 out of 25 statements that supported the early initiation of fixed combination treatment, if indicated in a meaningful number of their asthma and COPD patients.

Mechanism of thrombocytopenia in chronic hepatitis C as evaluated by the immature platelet fraction.

INTRODUCTION: Thrombocytopenia occurs frequently in chronic hepatitis C. The mechanism of this association was investigated utilizing the immature platelet fraction (IPF%) as an index of platelet production together with assay of thrombopoietin (TPO). METHODS: In a cross-sectional study, 47 patients with chronic hepatitis C were studied, 29 with thrombocytopenia and 18 without thrombocytopenia (six patients in each group were on interferon therapy). RESULTS: IPF% was elevated in the thrombocytopenic compared with the nonthrombocytopenic group (9.0 ± 4.8% vs. 4.7 ± 2.4%, P < 0.001), and an increase in IPF% was significantly associated with thrombocytopenia on multivariable analysis (P < 0.05). Splenomegaly was more common in thrombocytopenic than in nonthrombocytopenic subjects (66% vs. 6%, P < 0.001), and on multivariable analysis, splenomegaly was the factor associated with the highest relative risk of thrombocytopenia (RR = 1.9, P < 0.05). IPF% values were elevated in a similar proportion of thrombocytopenic patients with and without splenomegaly (58% and 60%, respectively). There was no difference in TPO levels between thrombocytopenic and nonthrombocytopenic patients, and TPO levels were not related to the risk of thrombocytopenia on multivariable analysis. Significantly more thrombocytopenic than nonthrombocytopenic subjects had abnormal liver function tests, cirrhosis, and portal hypertension, and a decrease in serum albumin was significantly associated with thrombocytopenia (P < 0.005) on multivariable analysis. CONCLUSIONS: Factors associated with liver disease in general are associated with thrombocytopenia in chronic hepatitis C. Peripheral platelet destruction or sequestration is the major mechanism for thrombocytopenia, with hypersplenism being an important cause. Low TPO levels were not related to the occurrence of thrombocytopenia in this study.

The pharmacokinetics of peginterferon alfa-2a and ribavirin in African American, Hispanic and Caucasian patients with chronic hepatitis C.

BACKGROUND: Amongst Caucasian, Hispanic and African Americans with genotype 1 hepatitis C virus (HCV), there is a wide variation in response to treatment with peginterferon alfa-2a (PEG-IFN alfa-2a) and ribavirin. AIM: To evaluate the pharmacokinetics (PK) of PEG-IFN alfa-2a and ribavirin among these three groups. METHODS: Forty-seven patients with genotype 1 CHC (17 African Americans, 14 Hispanics and 16 Caucasians) received 8 weeks of PEG-IFN alfa-2a (180 µg/week) and ribavirin (1000 or 1200 mg/day). PEG-IFN alfa-2a serum concentrations and ribavirin plasma concentrations were measured following the first dose and at week 8. Pharmacokinetic parameters (C(max), T(max), AUC, CL/F) were estimated using noncompartmental methods. RESULTS: There was no difference in the pharmacokinetic parameters for PEG-IFN alfa-2a following single-dose or steady-state administration between African American or Hispanic patients compared with Caucasian patients. Ribavirin pharmacokinetic parameters were similar between Hispanic and Caucasian patients for single-dose and steady-state administration. The single-dose C(max) was 33% lower (P < 0.05) in African American compared with Caucasian patients. Other ribavirin single-dose and steady-state pharmacokinetic parameters were slightly decreased (approximately 20% lower) in African American patients, but were not considered clinically meaningful. CONCLUSIONS: No differences were observed in PEG-IFN alfa-2a pharmacokinetic parameters between African American or Hispanic patients compared with Caucasian patients. For ribavirin, no differences were observed in pharmacokinetic parameters between Hispanic and Caucasian patients. While a trend towards increased ribavirin clearance and decreased exposure was observed in African American patients vs. Caucasian patients, the differences were small and not considered clinically meaningful (Clinical Trial Number: NP17354).

Impact of common KIBRA allele on human cognitive functions.

The rs17070145 polymorphism (C → T substitution, intron 9) of the KIBRA gene has recently been associated with episodic memory and cognitive flexibility. These findings were inconsistent across reports though, and largely lacked gene-gene or gene-environment interactions. The aim of the present study was to determine the impact of the rs17070145 polymorphism on clinically relevant cognitive domains and its interaction with the modifiers 'lifestyle' and 'cardiovascular risk factors'. Five-hundred forty-five elderly volunteers (mean age 64 years, ±7 years, 56% women) accomplished a comprehensive cognitive testing. Principal component analysis was used to reveal the internal structure of the data, rendering four composite scores: verbal memory, word fluency, executive function/psychomotor speed, and working memory. Lifestyle was assessed with a detailed questionnaire, age-associated risk factors by clinical interview and examination. There was no main effect of the rs17070145 genotype on any cognitive composite scores. However, we found worse performance in executive functions for T-allele carriers in the presence of arterial hypertension (ß=-0.365, p=0.0077 and 0.031 after Bonferroni correction). This association was further modified by gender, showing the strongest association in hypertensive females (ß=-0.500, p=0.0072 and 0.029 after Bonferroni correction). The effect of KIBRA on cognitive function seems to be complex and modified by gender and arterial hypertension.

Modeling effluent distribution and nitrate transport through an on-site wastewater system.

Properly functioning on-site wastewater systems (OWS) are an integral component of the wastewater system infrastructure necessary to renovate wastewater before it reaches surface or ground waters. There are a large number of factors, including soil hydraulic properties, effluent quality and dispersal, and system design, that affect OWS function. The ability to evaluate these factors using a simulation model would improve the capability to determine the impact of wastewater application on the subsurface soil environment. An existing subsurface drip irrigation system (SDIS) dosed with sequential batch reactor effluent (SBRE) was used in this study. This system has the potential to solve soil and site problems that limit OWS and to reduce the potential for environmental degradation. Soil water potentials (Psi(s)) and nitrate (NO(3)) migration were simulated at 55- and 120-cm depths within and downslope of the SDIS using a two-dimensional code in HYDRUS-3D. Results show that the average measured Psi(s) were -121 and -319 cm, whereas simulated values were -121 and -322 cm at 55- and 120-cm depths, respectively, indicating unsaturated conditions. Average measured NO(3) concentrations were 0.248 and 0.176 mmol N L(-1), whereas simulated values were 0.237 and 0.152 mmol N L(-1) at 55- and 120-cm depths, respectively. Observed unsaturated conditions decreased the potential for NO(3) to migrate in more concentrated plumes away from the SDIS. The agreement (high R(2) values approximately 0.97) between the measured and simulated Psi(s) and NO(3) concentrations indicate that HYDRUS-3D adequately simulated SBRE flow and NO(3) transport through the soil domain under a range of environmental and effluent application conditions.

Assessment of the 16S-23S rDNA intergenic spacer region in Enterococcus spp. for microbial source tracking.

A new library-based microbial source tracking (MST) approach intended for initial application in the coastal waters of Virginia was evaluated. Host-origin isolates of Enterococcus spp. were collected from beaches and the surrounding tidewater region of Virginia and used to construct a library based on the pattern of DNA band lengths produced by the amplification of the 16S-23S rDNA intergenic spacer (IGS) region, and subsequent digestion with MboI. Initial results from small host-origin libraries (64 and 200 total isolates) with discriminant analysis (DA) and logistic regression (LR) yielded high average rates of correct classification (ARCC) for a four-source classification split (birds, dogs, sewage, and wildlife), with ARCCs ranging from 83 to 100%. However, the poor results obtained when classification was attempted on a non-library validation set (VS, ARCCs of 47 and 48%, respectively, using DA and LR) demonstrated that a library of 200 isolates was insufficient to adequately represent the diversity of the enterococci in the sampled region. An increase in the library size to 1029 total isolates was accompanied by a reduction in the ARCC of the library to 42.7% with DA and 45.7% with LR, plus similarly poor results obtained from the VS. The low correct classification rates generated by the larger known-source library were unsuitable for field application. Many reported MST methods have been based on results obtained using small host-origin libraries without external validation. Our results indicate that such an approach can be very misleading, and that larger libraries and external validation is essential for the confirmation of preliminary results.

Microbial source tracking in a rural watershed dominated by cattle.

Antibiotic resistance analysis (ARA), frequency of sampling, and seasonality were evaluated in a rural Virginia watershed dominated by cattle. The selected watershed (Mill Creek) was 3767 ha in size, included two small communities (one sewered and one unsewered), and several farms that when combined contained over 3800 beef and dairy cattle. Monthly monitoring of fecal coliforms at two sampling sites in Mill Creek from January to December, 2001, revealed that the recreational standard (1000 colony forming units, CFUs/100 ml) was exceeded a total of eight times for a 33% violation rate at each site. In addition, stream samples were collected weekly for 4 consecutive weeks during seasonal high flows (March) and seasonal low flows (September-October), plus daily for 7 consecutive days within the weekly schedules for a combined total of 60 stream samples (30 at each of two sites). The recreational standard was exceeded once during seasonal high flow and nine times during seasonal low flow. Microbial source tracking (MST) was performed by ARA to assess the impact of cattle on water quality within the different sampling routines. The resistance patterns of 2880 water isolates and 1158 known source (host-origin) isolates were determined with seven antibiotics at 28 different concentrations. The 1158 isolate database was reduced to 562 unique isolates when clonal ARA patterns were removed. This database of 562 unique isolates had an average rate of correct classification (ARCC) of 95.4%, and several statistical procedures confirmed the library as accurate and representative. Sixty-five percent of 50 challenge-set isolates from sources, but not samples, used in the library were correctly identified. The 562 unique pattern database was used to classify Escherichia coli isolates from water samples into six host source categories. The ARA results showed that cattle were the major source of pollution in the stream and cattle were the dominant source in over 60% of the water samples. Sampling frequency and seasonality had no effect on the MST results, as cattle dominated both seasons and samplings. Deer were a minor contributor in the summer (high water demand), and geese were a minor contributor in the winter when migratory flocks were observed moving through the watershed. An unexpected human allocation was found, especially under seasonal high flow conditions. The exact origin of this human allocation is not known. This project demonstrated that a host-origin library, based on a phenotypic method, could be developed for a well-defined watershed and was both representative of the sources in the watershed and performed reasonably well against a challenge set.

Detection and remediation of human-origin pollution at two public beaches in Virginia using multiple source tracking methods.

Two public beaches (Anderson and Hilton) in Newport News, Virginia, were frequently closed to swimming in 2004 due to high Enterococcus spp. counts that exceeded the regulatory standard. The microbial source tracking (MST) methods of antibiotic resistance analysis (ARA) and fluorometry (to detect optical brighteners) were used in the summer of 2004 to determine the origins of fecal pollution at the two beaches. Both MST methods detected substantial human-origin pollution at the two beaches, in locations producing consistently high levels of Enterococcus spp. Investigations by municipal officials led to the fluorometric detection and subsequent repair of sewage infrastructure problems at both beaches. The success of the mitigation efforts was confirmed during the summer of 2005 using ARA and fluorometry, with the results cross-validated by pulsed-field gel electrophoresis (PFGE).

Black patients with chronic hepatitis C have a lower sustained viral response rate than non-Blacks with genotype 1, but the same with genotypes 2/3, and this is not explained by more frequent dose reductions of interferon and ribavirin*.

In previous hepatitis C virus (HCV) treatment studies, Black patients not only had a lower sustained viral response (SVR) rate to interferon and ribavirin (RBV) than non-Black patients but also a higher frequency of HCV genotype 1 (GT-1) infection. The aim of this community-based study was to determine whether Black patients have a lower SVR rate independent of genotype. We prospectively enrolled 785 patients (24.8% Black, 71.5% White, 3.7% others) who received interferon alpha-2b 3 MU three times weekly + RBV 1000-1200 mg/day for 24 weeks (GT-2/3) or 48 weeks (GT-1). Black patients were more commonly infected with GT-1 (86.8%vs 64.8%, P < 0.001) and less frequently had an SVR compared with non-Black patients (8.4%vs 21.6%, P < 0.001). Within GT-1, Black patients had a lower SVR rate than non-Black patients (6.1%vs 14.1%, P = 0.004) but not within GT-2/3 (50.0%vs 36.5%, P = 0.47). Black patients had lower baseline haemoglobin levels (14.8 vs 15.3 g/dL, P < 0.001) and neutrophil counts (2900 vs 4100/mm(3), P < 0.001) and required more frequent dose reductions of RBV (29.8%vs 18.5%, P < 0.001) and interferon (4.7%vs 1.6%, P = 0.012). However, dose reductions were not associated with lower SVR rates while early treatment discontinuations were (2.9%vs 25.7%, P < 0.001). Independent predictors of SVR were GT-1 [odds ratio (OR) 0.33; 95% confidence interval (CI) 0.20-0.55; P < 0.001], Black race (OR 0.45; 95% CI 0.22-0.93; P = 0.030), and advanced fibrosis, stages 3 + 4 (OR 0.53; 95% CI 0.31-0.92; P = 0.023). In conclusion, Black patients infected with HCV GT-1 (but not GT-2/3) have a lower SVR rate than non-Black patients. This is not explained by their lower baseline haemoglobin levels and neutrophil counts that lead to higher rates of ribavirin and interferon dose reductions.

A mutant of eukaryotic protein synthesis initiation factor eIF4E(K119A) has an increased binding affinity for both m7G cap analogues and eIF4G peptides.

The eukaryotic multisubunit initiation factor eIF4F is an essential component of the translational machinery. Recognition of the cap structure of mRNA, m(7)GpppN, where N is any nucleotide, by eIF4E is required for initiation of translation. Here we compare the equilibrium and thermodynamic binding characteristics of wild-type eIF4E and a high-affinity mutant, eIF4E(K119A), with those of cap analogues and eIF4G peptides. The temperature-dependent K(d) values for cap analogues were markedly lower, indicating tighter binding, with the eIF4E(K119A) mutant compared with wild-type eIF4E. Although interactions with cap analogues were found to be enthalpically driven, entropic contributions were also significant. Moreover, the binding affinities of eIF4G peptides were 2-4-fold tighter for eIF4E(K119A) than for eIF4E(wt). These results demonstrate that the binding affinity for both the mRNA cap and eIF4G peptides can be simultaneously altered by point mutations distant from either binding site. Entropic contributions to binding suggesting hydrophobic interactions are larger in the mutant protein and are most likely due to a conformational change.

Carbon source utilization profiles as a method to identify sources of faecal pollution in water.

AIMS: Carbon source utilization profiles as a phenotypic fingerprinting methodology for determining sources of faecal pollution in water were evaluated. METHODS AND RESULTS: Three hundred and sixty-five Enterococcus isolates were collected from known faecal sources in four different geographical regions and were identified to species with the commercial Biolog system. Discriminant analysis (DA) was used to identify the substrate-containing wells that best classified the 365 isolates by source. By using 30 of the 95 wells for the analysis, the average rate of correct classification (ARCC) by source was 92.7% for a human vs non-human two-way classification when isolates from all regions were combined into one library. Corresponding ARCCs for other classification schemes were 81.9% for a four-way classification of human vs livestock vs wildlife vs domestic pets, and 85.7% for a three-way classification without human isolates. When three individual libraries were made based on classification of sources within Enterococcus species, the ARCC was 95.3% for the Ent. faecalis library, 95.8% for the Ent. gallinarum library and 94.7% for the Ent. mundtii library. Thirty Enterococcus isolates (unknown sources) were obtained from each of three stream sites where a specific source of pollution was apparent; 90.0% of the isolates from a human-suspected source were classified as human, 86.6% were classified as livestock from a livestock-suspected site, and 93.3% were classified as wildlife from a wildlife-suspected site. CONCLUSIONS: Phenotypic fingerprinting with carbon source utilization profiles provided levels of correct classification by sources from an Enterococcus library that were in the upper range of those reported in the literature. ARCCs for three Enterococcus species-specific libraries were very high and may be the best approach for further developing this concept and methodology. SIGNIFICANCE ANC IMPACT OF THE STUDY: The results, based on a modest Enterococcus library and a preliminary field validation test, demonstrated the potential for carbon source utilization profiles to be employed as a phenotypic method for determining sources of faecal pollution in water.

Abdominal spiral CT in children: which radiation exposure is required?

We decided to test to what extent dose reduction is possible in abdominal spiral computed tomography (CT) in young children without loss of anatomic diagnostic information. A retrospective study was performed of 30 abdominal CT examinations of children aged 3 months to 7 years. These were divided into two groups: group A with reduced radiation exposure (tube current 50 mA, CT dose index CTDIFDA < or =0.83 mGy) and group B with standard radiation exposure (tube current > or =100 mA, CTDIFDA > or =1.66 mGy). Image quality was assessed using a four-part scale ('excellent', 'good', 'sufficient', 'poor') on visual image impression and visibility of 32 anatomical details. Five experienced radiologists read the CT scans independently who were blinded to the examination parameters. Differences in ranked data were evaluated with Wilcoxon's rank sum test. No difference between groups A and B was observed in visual image impression. Detail visibility was significantly lower in group A, but the differences were limited to right upper quadrant structures (portal vein, common bile duct, pancreatic head, adrenals) and to arterial branches. Significant differences in visibility rated as 'poor' were only found for the hepatic, splenic and renal arteries; all other structures showed no difference between groups A and B. A protocol with reduced radiation exposure (50 mA, CTDIFDA < or =0.83 mGy) allowed the demonstration of most anatomic structures in abdominal spiral CT in young children. For the precise demonstration of small details (e.g. structures of the right upper quadrant), a protocol with standard radiation exposure (> or =100 mAs) was superior.

Reduced FMRP and increased FMR1 transcription is proportionally associated with CGG repeat number in intermediate-length and premutation carriers.

The 5' untranslated CGG repeat in the fragile X mental retardation-1 (FMR1) gene is expanded in families with fragile X syndrome, with more than 200 CGGs resulting in mental retardation due to the absence of the encoded fragile X mental retardation protein (FMRP). Intermediate and premutation alleles, containing between approximately 40 and 200 repeats, express grossly normal FMRP levels and such carriers are widely believed to be non-penetrant, despite continued reports of subtle cognitive/psychosocial impairment and other phenotypes. Using a highly sensitive quantification assay, we demonstrate significantly diminished FMRP levels in carriers, negatively correlated with repeat number. Despite reduced FMRP, these carrier alleles overexpress FMR1, resulting in a positive correlation between repeat number and FMR1 message level. These biochemical deviations associated with intermediate and premutation FMR1 alleles, found in approximately 4% of the population, suggest that the phenotypic spectrum of fragile X syndrome may need to be revisited.

Trapping-mediated dissociative chemisorption of cycloalkanes on Ru(001) and Ir(111): influence of ring strain and molecular geometry on the activation of C-C and C-H bonds.

We have measured the initial probabilities of dissociative chemisorption of perhydrido and perdeutero cycloalkane isotopomers on the hexagonally close-packed Ru(001) and Ir(111) single-crystalline surfaces for surface temperatures between 250 and 1100 K. Kinetic parameters (activation barrier and preexponential factor) describing the initial, rate-limiting C-H or C-C bond cleavage reactions were quantified for each cycloalkane isotopomer on each surface. Determination of the dominant initial reaction mechanism as either initial C-C or C-H bond cleavage was judged by the presence or absence of a kinetic isotope effect between the activation barriers for each cycloalkane isotopomer pair, and also by comparison with other relevant alkane activation barriers. On the Ir(111) surface, the dissociative chemisorption of cyclobutane, cyclopentane, and cyclohexane occurs via two different reaction pathways: initial C-C bond cleavage dominates on Ir(111) at high temperature (T > approximately 600 K), while at low temperature (T < approximately 400 K), initial C-H bond cleavage dominates. On the Ru(001) surface, dissociative chemisorption of cyclopentane occurs via initial C-C bond cleavage over the entire temperature range studied, whereas dissociative chemisorption of both cyclohexane and cyclooctane occurs via initial C-H bond cleavage. Comparison of the cycloalkane C-C bond activation barriers measured here with those reported previously in the literature qualitatively suggests that the difference in ring-strain energies between the initial state and the transition state for ring-opening C-C bond cleavage effectively lowers or raises the activation barrier for dissociative chemisorption via C-C bond cleavage, depending on whether the transition state is less or more strained than the initial state. Moreover, steric arguments and metal-carbon bond strength arguments have been evoked to explain the observed trend of decreasing C-H bond activation barrier with decreasing cycloalkane ring size.

Modifications of eukaryotic initiation factor 4F (eIF4F) in adult cardiocytes by adenoviral gene transfer: differential effects on eIF4F activity and total protein synthesis rates.

In adult feline cardiocytes, increases in eukaryotic initiation factor 4F (eIF4F) activity are correlated with accelerated rates of total protein synthesis produced in response to increased load. Adenoviral gene transfer was employed to increase either eIF4F complex formation or the phosphorylation of eIF4E on Ser-209. To simulate load,cardiocytes were electrically stimulated to contract (2 Hz,5 ms pulses). Non-stimulated cardiocytes were used as controls.Adenovirus-mediated overexpression of wild-type eIF4E increased the total eIF4E pool by 120-140% above endogenous levels after 24 h and produced a corresponding increase in eIF4F content.However, it did not accelerate total protein synthesis rates inquiescent cardiocytes; neither did it potentiate the increase produced by contraction. To modify the affinity of eIF4F, cardiocytes were infected with a mutant (eIF4E/W56F) with a decreased binding affinity for the mRNA cap. Overexpression of eIF4E/W56F increased the quantity of eIF4F but the rate of total protein synthesis was decreased inquiescent and contracting cardiocytes. Overexpression of a mutant that blocked eIF4E phosphorylation (eIF4E/S209A) increased the quantity ofeIF4F without any significant effect on total protein synthesis rates in quiescent or contracting cardiocytes. Overexpression of the eIF4Ekinase Mnk-1 increased eIF4E phosphorylation without a corresponding increase in eIF4F complex formation or in the rate of total protein synthesis. We conclude the following: (1) eIF4F assembly is increased by raising eIF4E levels via adenoviral gene transfer; (2) the capbinding affinity of eIF4F is a rate-limiting determinant for total protein synthesis rates; and (3) increases in the quantity of eIF4Falone or in eIF4E phosphorylation are not sufficient to accelerate total protein synthesis rates.