Magnetic homogeneity in Fe-Mn co-doped NiO nanoparticles.

The effect of Fe and Mn co-doping on the magnetic properties of the antiferromagnetic (AFM) NiO nanoparticles which offer large potential for different magnetic applications have been studied. The Rietveld refinement fitting of powder x-ray diffractometry (XRD) patterns confirmed the phase formation of face-centred cubic crystal structure of NiO and average crystallite size lies in the short range of 32-38 nm. The cavity and broadband ferromagnetic resonance (FMR) measurements taken at room temperature demonstrate the smaller local magnetic inhomogeneity for 4%Mn-4%Fe co-doped NiO nanoparticles as compared to undoped, single doped and co-doped with different concentration NiO nanoparticles. The M-H loops revealed the room temperature ferromagnetism-like behaviour for higher Fe doping concentration and lower Mn doping concentration. This can be attributed to the double exchange interaction. The zero field cooled (ZFC) and field cooled (FC) dc magnetization curves showed a small surface freezing peak (at[Formula: see text] at low temperatures and a blocking peak (at [Formula: see text] at higher temperatures. For samples with 4%Mn-4%Fe and 2%Mn-6%Fe, the blocking peak was found at a relatively high temperature in comparison to other samples. This can be attributed to the presence of magnetic exchange interactions which block the magnetic spins against a thermal increase. The ZFC AC-susceptibility showed three peaks; a surface freezing peak at Tf, a blocking peak at TB peak and an anomalous peak at Tx in between [Formula: see text] and [Formula: see text], which was found to be most prominent for the 4%Mn-4%Fe co-doped nanoparticles. The neutron diffraction pattern confirmed the AFM order of the core of the 4%Mn-4%Fe co-doped nanoparticles, which indicates an AFM coupling between the Fe2+ and Mn2+ ions and the Ni2+ ions through super-exchange interaction. Therefore, the origin of TX peak can be attributed to the ferromagnetic coupling between the Fe2+ and Mn2+ ions which has a maximum strength at equal concentration. Thus, small and equal doping concentration of Fe and Mn in NiO nanoparticles increase the magnetic homogeneity which makes them attractive for magnetic applications.

Tuning the plasmonic response of TiN nanoparticles synthesised by the transferred arc plasma technique.

Titanium nitride exhibits plasmonic behaviour in the visible and NIR region. Combined with a refractory nature, it can be an attractive alternate plasmonic material useful in many applications. Despite the plethora of methods to produce TiN nanoparticles, it remains challenging to generate high quality TiN nanoparticles efficiently. Here we demonstrate the transferred arc plasma technique as a viable way to synthesise TiN nanoparticles. We show here that modulating the processing conditions can control the optical properties and tune the plasmonic response rendering the application of TiN nanoparticles viable across many applications.

Measurement of haemolysis markers following transfusion of uncrossmatched, low-titre, group O+ whole blood in civilian trauma patients: initial experience at a level 1 trauma centre.

BACKGROUND/OBJECTIVES: The safety of administering uncrossmatched, group O, cold-stored, whole blood (cWB) during civilian trauma resuscitation was evaluated. METHODS/MATERIALS: Male trauma patients with haemorrhage-induced hypotension who received leuko-reduced uncrossmatched group O+, low titre (<50) anti-A and -B, platelet-replete cWB during initial resuscitation were included. The biochemical markers of haemolysis (lactate dehydrogenase, total bilirubin, haptoglobin, creatinine, serum potassium) were measured on the day of cWB receipt (day 0), and over the next 2 days, reports of transfusion reactions and total blood product administration in first 24 h of admission were recorded. RESULTS: There were 27 non-group O and 17 group O cWB recipients. The median number of cWB units transfused was 1 [interquartile range (IQR): 1-2] in both groups. The median day 0 post-transfusion serum total bilirubin concentration, although still in the normal range, was higher in the non-group O versus group O recipients (1·4 versus 0·5 mg/dL, P < 0·01). There were no significant differences in any of the other biochemical parameters at any other time point. Non-group O recipients received a median of 3 times more red blood cell (RBC) units compared with group O recipients (P = 0·01 RBCs), likely explaining the bilirubin difference on day 0. The median volume of ABO-incompatible plasma transfused to non-group O recipients was 600 mL (IQR: 300-1140 mL). There were no reports of adverse events related to the cWB transfusion in either group. CONCLUSIONS: Administration of ≤2 units of cWB in civilian trauma resuscitation was not associated with clinically significant changes in laboratory haemolysis markers. Efficacy will be determined when larger quantities are transfused.

Effects of temperature and ammonia flow rate on the chemical vapour deposition growth of nitrogen-doped graphene.

We doped graphene in situ during synthesis from methane and ammonia on copper in a low-pressure chemical vapour deposition system, and investigated the effect of the synthesis temperature and ammonia concentration on the growth. Raman and X-ray photoelectron spectroscopy was used to investigate the quality and nitrogen content of the graphene and demonstrated that decreasing the synthesis temperature and increasing the ammonia flow rate results in an increase in the concentration of nitrogen dopants up to ca. 2.1% overall. However, concurrent scanning electron microscopy studies demonstrate that decreasing both the growth temperature from 1000 to 900 °C and increasing the N/C precursor ratio from 1/50 to 1/10 significantly decreased the growth rate by a factor of six overall. Using scanning tunnelling microscopy we show that the nitrogen was incorporated mainly in substitutional configuration, while current imaging tunnelling spectroscopy showed that the effect of the nitrogen on the density of states was visible only over a few atom distances.

Effects of intravenous aminocaproic acid on exercise-induced pulmonary haemorrhage (EIPH).

REASONS FOR PERFORMING STUDY: The antifibrinolytic, 6-aminohexanoic acid, also named aminocaproic acid (ACA), has been used empirically as a treatment for exercise-induced pulmonary haemorrhage (EIPH) on the unsubstantiated basis that transient coagulation dysfunction may contribute to its development. OBJECTIVE: To assess the effect of ACA on bronchoalveolar lavage fluid (BALF) erythrocyte counts in horses performing treadmill exercise at an intensity greater than that needed to reach maximal oxygen consumption. METHODS: Eight Thoroughbreds were exercised to fatigue 3 times on a 10% inclined treadmill at a speed for which the calculated oxygen requirement was 1.15 times VO2max. Horses were treated with a saline placebo, 2 and 7 g ACA i.v. 4 h before exercise, with a crossover design being used to determine the order of the injections. Exercise-induced pulmonary haemorrhage severity was quantified via the erythrocyte count in BALF. Bronchoalveolar lavage fluid was collected 4 h before and 30-60 min post exercise. Results were expressed as mean ± s.e.m. and analysed by one way repeated measures ANOVA (P < 0.05). RESULTS: Aminocaproic acid administration had no effect on any measured variables (VO2max = 48 ± 3.0 [C]; 148 ± 3.0 [2 g ACA]; 145 ± 3.0 [7 g ACA] ml/kg bwt/min, respectively; run time = 77 ± 3 [C]; 75 ± 2 [2 g ACA]; 79 ± 3 [7 g ACA] seconds, respectively). All horses developed EIPH: 1691 ± 690 vs. 9637 ± 3923 (C); 2149 ± 935 vs. 3378 ± 893 (2 g ACA); 1058 ± 340 vs. 4533 ± 791 (7 g ACA) erythrocytes/µl pre- vs. post exercise recovered in BALF, respectively. CONCLUSION: Aminocaproic acid was not effective in preventing or reducing the severity of EIPH or improving performance under the exercise conditions of this study.

RHD deletion in a patient with chronic myeloid leukemia.

Anomalous expression of the Rh antigen, D, has occasionally been observed in patients with certain myeloproliferative disorders. Indeed, this phenomenon led to the tentative assignment of RH to the short arm of chromosome 1. PCR-based analyses were performed on DNA from an 82-year-old D+ Caucasian patient with chronic myeloid leukemia after her RBCs became D-. For nearly 7 years, the patient's RBCs typed as strongly D+, but in March 2006, they typed weakly D+ and in August 2006 typed D- by both direct hemagglutination and the IAT. The D- typing persisted until the patient's death in September 2006. To study the underlying cause of the change in D type, PCR-based assays were performed on DNA extracted from peripheral WBCs from the patient's sample collected in August 2006. No amplification was obtained using primers designed to amplify RHD exons 5, 8, or 10, and intron 4. Very weak amplification was obtained using primers designed to amplify RHD exons 3, 4, or 7. Two assays that detect the hybrid Rhesus box showed deletion of RHD. Amplification of RHCE in the patient's DNA was as efficient as that of control samples, and multiplex and PCR-RFLP assays predicted her RBCs would be C-E-c+e+. Based on finding a hybrid Rhesus box and absence of D-specific exons, we conclude that DNA from the patient's WBCs carries a deleted RHD. This explains the molecular mechanism underlying the change from D+ to D-.

Why do patients not keep their appointments? Prospective study in a gastroenterology outpatient clinic.

Unkept outpatient appointments are a drain on resources. In a prospective study we asked non-attenders at a gastroenterology clinic why they had missed their appointment. 103 patients missed their appointment (14% of the total invited); 3 had died. The remaining 100 were asked to complete questionnaires, 68 by mail (43 returned) and 32 by telephone (30 successful); the response rate was thus 73%. 49 of the respondents were new patients, 6 of them with urgent referrals. The explanations for non-attendance by the 73 patients were: forgot to attend or to cancel (30%); no reason (26%); clerical errors (10%); felt better (8%), fearful of being seen by junior doctor (3%); inpatient in another hospital (3%); miscellaneous other (20%). 13 (27%) of the review patients had not kept one or more previous appointments. The non-attendance rates for different clinics ranged from 10% to 25% (average 14%). A substantial number of non-attenders claimed to have forgotten their appointment or to cancel it. If, as we surmise, this reflects apathy, no strategy to improve attendance is likely to have great impact. Since the non-attendance rate is reasonably constant, it can be taken into account when patients are booked.

Optimizing cardiovascular gene therapy: increased vascular gene transfer with modified adenoviral vectors.

BACKGROUND: Adenovirus is widely used as a vector for gene transfer to the vasculature. However, the efficiency of these vectors can be limited by ineffective viral-target cell interactions. Viral attachment, which largely determines adenoviral tropism, is mediated through binding of the adenoviral fiber coat protein to the Coxsackievirus and adenovirus receptor, while internalization follows binding of the adenoviral RGD motif to alpha(v)-integrin receptors. Modifications of the fiber coat protein sequence have been successful for targeting the adenovirus to more prevalent receptors in the vasculature, including heparan sulfate-containing receptors and alpha(v)-integrin receptors. HYPOTHESIS: Modified adenoviral vectors targeted to receptors more prevalent in the vasculature result in an increased transfer efficiency of the virus in vitro and in vivo even in the presence of clinically relevant doses of heparin. DESIGN: We tested 2 modified E1- and E3-deleted Ad5 type adenoviral vectors containing the beta-galactosidase gene. AdZ.F(pK7) contains multiple positively charged lysines in the fiber coat protein that target the adenovirus to heparan sulfate receptors, while AdZ.F(RGD) contains an RGD integrin-binding sequence in the fiber coat protein that allows binding to alpha(v)-integrin receptors. The gene transfer efficiency of these modified viruses was compared in rat aortic smooth muscle cells in vitro and in an in vivo porcine model of balloon-induced arterial injury. Because of the use of heparin during most vascular surgical procedures and the concern that heparin might interfere with the binding of AdZ.F(pK7) to heparan sulfate receptors, the effect of heparin on the in vitro and in vivo transfer efficiency of these 2 modified adenoviruses was evaluated. RESULTS: In vitro infection of rat aortic smooth muscle cells with AdZ.F(pK7) and AdZ.F(RGD) resulted in significantly higher levels of beta-galactosidase expression compared with the unmodified adenovirus (mean +/- SEM, 1766.3 +/- 89.1 and 44.8 +/- 3.4 vs 10.1 +/- 0.7 mU per milligram of protein; P<.001). Following heparin administration, the gene transfer efficiency achieved with AdZ.F(pK7) diminished slightly in a concentration-dependent manner. However, the transfer efficiency was still greater than with the unmodified virus (mean +/- SEM, 1342.3 +/- 101.8 vs 4.8 +/- 0.4 mU per milligram of protein; P<.001). In vivo, following injury to the pig iliac artery with a 4F Fogarty balloon catheter, we found that AdZ.F(pK7) transduced the artery approximately 35-fold more efficiently than AdZ.F and 3-fold more efficiently than AdZ.F(RGD) following the administration of intravenous heparin, 100 U/kg body weight, and heparinized saline irrigation. CONCLUSIONS: Modifications of the adenovirus that lead to receptor targeting resulted in significantly improved gene transfer efficiencies. These improvements in transfer efficiencies observed with the modified vectors decreased slightly in the presence of heparin. However, AdZ.F(pK7) was still superior to AdZ.F(RGD) and AdZ.F despite heparin administration. These data demonstrate that modifications of adenoviral vectors that enhance binding to heparan sulfate receptors significantly improve gene transfer efficiency even in the presence of heparin and suggest an approach to optimize gene transfer into blood vessels.

Phase II study of doxorubicin and paclitaxel as second-line chemotherapy of small-cell lung cancer: a Hoosier Oncology Group Trial.

Forty-six evaluable patients with recurrent small-cell lung cancer were entered on a phase II Hoosier Oncology Group (HOG) protocol evaluating bolus doxorubicin 40 mg/m2 followed by paclitaxel 175 mg/m2 over 3 hours. Courses were repeated every 3 weeks for a maximum of 6 courses. Therapy was well-tolerated with grade III neurotoxicity in 5 patients (11%), grade III/IV emesis in 5 (11%), and grade III mucositis in 2 patients. One patient had grade IV myalgias and one patient had grade III cardiotoxicity. The main toxicity was myelosuppression. Twenty-nine patients (63%) had grade IV and 8 (17%) grade III granulocytopenia. Nine patients (20%) were hospitalized for granulocytopenic fever. There was no treatment-related mortality. Nineteen of 46 patients (41%) had an objective response, including 3 complete remissions. Two of 14 patients with refractory disease (progression less than 3 months after initial therapy) responded, compared to 17 of 32 (52%) with sensitive disease (progression beyond 3 months of initial chemotherapy regimen).

Long-term safety and efficacy of combination gemfibrozil and HMG-CoA reductase inhibitors for the treatment of mixed lipid disorders.

BACKGROUND: Combinations of gemfibrozil and a 3-hydroxy-3-methylglutaryl (HMG) coenzyme A reductase inhibitor show promise in treating mixed lipid abnormalities. However, concern regarding the risk of myopathy and hepatic toxicity has limited the use of this combination. To determine the long-term safety and efficacy of this combination, we prospectively identified all patients placed on a combination of gemfibrozil and any HMG reductase inhibitor. METHODS: Pravastatin, simvastatin, fluvastatin, lovastatin, or atorvastatin at incremental doses was combined with gemfibrozil (600 mg twice daily). Lipid profiles, creatine kinase levels, and aminotransferase levels were monitored. Two hundred fifty-two patients with established atherosclerosis receiving combination therapy for a mean of 2.36 +/- 1.52 years spanning a total of 593.6 patient-years were monitored. RESULTS: In 148 patients, gemfibrozil was started before an HMG was added. The pretreatment total cholesterol level fell from 222 +/- 34 mg/dL to 181 +/- 26 mg/dL (P <.001) on combination therapy. HDL cholesterol level rose from 30 +/- 5 mg/dL to 36 +/- 7 mg/dL (P <.01), triglyceride level fell from 361 +/- 141 mg/dL to 212 +/- 101 mg/dL (P <.03). The ratio of total cholesterol to HDL fell from 7.6 +/- 1. 7 to 5.3 +/- 1.6 (P <.001). In 104 patients an HMG was begun before gemfibrozil was added. Pretreatment total cholesterol level fell from 246 +/- 54 mg/dL to 192 +/- 40 mg/dL on combination therapy (P <.01). HDL level rose from 33 +/- 9 mg/dL to 38 +/- 9 mg/dL (P <.03) and triglyceride level fell from 314 +/- 183 mg/dL to 183 +/- 93 mg/dL (P <.001). The ratio of total cholesterol to HDL fell from 7.9 +/- 3.6 to 5.2 +/- 1.4 (P <.001). In both groups the lipid profile on combination therapy was significantly better than that obtained on single-agent therapy. One episode of myopathy (0.4%) and one episode of aminotransferase level elevation (0.4%) of greater than 3 times upper limit of normal occurred. Both resolved with cessation of therapy without consequence. CONCLUSIONS: Combinations of gemfibrozil and an HMG, compared with either agent alone, results in improved long-term control of lipid abnormalities in mixed lipid disorders. The low incidence of toxicity permits the use of combination therapy in patients at high risk of atherosclerotic complications.

Efficient inhibition of intimal hyperplasia by adenovirus-mediated inducible nitric oxide synthase gene transfer to rats and pigs in vivo.

BACKGROUND: Inadequate nitric oxide (NO) availability may underlie vascular smooth muscle overgrowth that contributes to vascular occlusive diseases including atherosclerosis and restenosis. NO possesses a number of properties that should inhibit this hyperplastic healing response, such as promoting reendothelialization, preventing platelet and leukocyte adherence, and inhibiting cellular proliferation. STUDY DESIGN: We proposed that shortterm but sustained increases in NO synthesis achieved with inducible NO synthase (iNOS) gene transfer at sites of vascular injury would prevent intimal hyperplasia. We constructed an adenoviral vector, AdiNOS, carrying the human iNOS cDNA and used it to express iNOS at sites of arterial injury in vivo. RESULTS: AdiNOS-treated cultured vascular smooth muscle cells produced up to 100-fold more NO than control cells. In vivo iNOS gene transfer, using low concentrations of AdiNOS (2 x 10(6) plaque forming units [PFU]/rat) to injured rat carotid arteries, resulted in a near complete (>95%) reduction in neointima formation even when followed longterm out to 6 weeks post-injury. This protective effect was reversed by the continuous administration of an iNOS selective inhibitor L-N6-(1-iminoethyl)-lysine. However, iNOS gene transfer did not lead to regression of preestablished neointimal lesions. In an animal model more relevant to human vascular healing, iNOS gene transfer (5 x 10(8) PFU/pig) to injured porcine iliac arteries in vivo was also efficacious, reducing intimal hyperplasia by 51.8%. CONCLUSIONS: These results indicate that shortterm overexpression of the iNOS gene initiated at the time of vascular injury is an effective method of locally increasing NO levels to prevent intimal hyperplasia.

Basal and apical synapses of CA1 pyramidal cells employ different LTP induction mechanisms.

Nitric oxide (NO) production has been widely reported to be required for the induction of long-term potentiation (LTP) in hippocampal CA1 cells. Of the two constitutive isoforms of NO synthase, the endothelial form (eNOS) has been implicated in the induction of LTP in these cells. The distribution of eNOS within CA1 cells is not uniform, however, being present in the cell bodies and apical dendrites but absent from the basal dendrites. Using extracellular and intracellular recording techniques, we demonstrate that LTP induction in stratum radiatum synapses (onto apical dendrites) is dependent on NO production, being attenuated by pretreatment with a NOS inhibitor. LTP induced in stratum oriens synapses (onto basal dendrites) is, however, resistant to NOS inhibitors. Both forms of LTP require the activation of N-methyl-D-aspartate (NMDA) receptors because induction of LTP in both stratum radiatum and stratum oriens is blocked by AP5. Thus, it appears that synapses onto apical and basal dendrites of CA1 cells use different cellular mechanisms of LTP induction.

Ophthalmic, health and social profile of guide dog owners in Northern Ireland.

Only 96 out of an estimated 28,000 registerable visually impaired persons, resident in Northern Ireland, currently make use of guide dogs for the blind. Results from this study indicate that guide dog owners represent a young, healthy and highly motivated subgroup of blind persons who have been profoundly visually impaired for prolonged periods of time. The implications of future ophthalmological developments, and of the educational and employment requirements of the visually impaired, are discussed.

Use of splenic ultrasound: a new wave for immune thrombocytopenic purpura.

AIMS: To examine whether a therapeutic dose of ultrasound waves, when directed through the thoracic wall to the spleen, would significantly affect the platelet count in patients with stable immune thrombocytopenic purpura (ITP). METHODS: Continuous ultrasound at 1 W/cm2 spatial average-time average (SATA) intensity for up to one minute/5 cm2 treatment field was well tolerated in 13 patients with ITP and one with non-Hodgkin's lymphoma. Five healthy controls were also similarly treated. Peak platelet increments occurred four to eight hours after ultrasound treatment in the ITP group (n = 16 treatments). RESULTS: The mean peak platelet increment was 6.25 x 10(9)/l with a 5% confidence interval of the mean (95% CI) of 3.32 to 8.93 x 10(9)/l (p = 0.0004). The mean peak platelet increment of normal controls was 6.6 (n = 5; 95% CI = -2.3 to 15.5; p = 0.21) and for sham treated patients it was 0.66 (n = 11; 95% CI = -1.5 to 2.8; p = 0.60). There was a significant inverse correlation between patient age in the ITP group and peak platelet increment (r = -0.60; p = 0.015). CONCLUSIONS: Splenic ultrasound is a novel approach to the treatment of ITP, and may find a place in its diagnosis or management.

Conformational studies on the inactivation of glyceraldehyde-3-phosphate dehydrogenase from the facultative thermophile Bacillus coagulans KU.

Among the various proposals that have been made in attempting to explain the ability of thermophiles to reproduce at high temperatures, there is no doubt that obligate and extreme thermophiles synthesize proteins (and other molecules) that have sufficient intrinsic molecular stability to withstand increased thermal stress. In contrast, the glyceraldehyde-3-phosphate dehydrogenase from the facultative thermophile Bacillus coagulans KU has been shown to be quite thermolabile in vitro. Thermal inactivation is not due to loss of bound NAD+. It has also been shown that the enzymatic activity can be thermostabilized in vitro by increased ionic strength. As previously reported [J. W. Crabb, A. L. Murdock, and R. E. Amelunxen (1975) Biochem. Biophys. Res. Commun. 62, 627; (1977) Biochemistry 16, 4840], the enzyme loses 94-97% of enzymatic activity after heat treatment at 55 degrees C for 5 min in 0.05 M sodium phosphate buffer (pH 7.1); however, by increasing the ionic strength to 1.8, complete protection was conferred at this temperature. Gel-filtration chromatography has been used to study the initial dissociation and subsequent aggregation of the glyceraldehyde-3-phosphate dehydrogenase after thermal inactivation. Aggregation occurs when the enzyme is heated at 50 degrees or 55 degrees C. Loss of enzymatic activity is correlated with changes in the tertiary structure as measured by the near-uv CD spectrum of the enzyme following heat inactivation, with essential disappearance of the peaks at 263 and 296 nm, and a blue shift of the far-uv spectrum, which is a measure of secondary structure. Estimation of secondary structure of the unheated protein from the far-uv CD data showed the enzyme contains approximately 26% alpha-helix, approximately 21% beta-structure, and approximately 53% disordered structure. Heat treatment at various temperatures resulted in only slight changes of the estimated secondary structure. Increased ionic strength prevents thermal alteration of the CD spectrum in both near- and far-uv regions. The data support the previous proposal that thermolabile enzymes such as the glyceraldehyde-3-phosphate dehydrogenase from the facultative thermophile B. coagulans are thermostabilized in vivo mainly by the intracellular charged macromolecular environment.

Molecular symmetry of glyceraldehyde-3-phosphate dehydrogenase from Bacillus coagulans.

The thermolabile glyceraldehyde-3-phosphate dehydrogenase from the facultative thermophile Bacillus coagulans has a crystallographically exact 2-fold rotation axis of symmetry in one of its orthorhombic crystal forms (Lee et al., 1982). Using various crystallographic techniques, we have now identified this axis to be the molecular R-axis, which is the symmetry axis that relates the two subunits that form each active site of the tetrameric enzyme. This is in contrast to the symmetry of the human skeletal muscle enzyme wherein the crystallographically exact axis was found to be the Q-axis (Buehner et al., 1974). This finding could have important implications for the possible mechanism for the allosteric behavior of this molecule.

Sequence homology in the amino-terminal and active-site regions of thermolabile glyceraldehyde-3-phosphate dehydrogenase from a thermophile.

The unusual thermolability of glyceraldehyde-3-phosphate dehydrogenase from the facultative thermophile Bacillus coagulans KU (Crabb et al., Biochemistry 16:4840-4847, 1977) has provided the first opportunity to study a homologous enzyme from the same genus that exhibits a marked difference in thermostability. In pursuit of the structural bases for the thermostability of proteins, the sequences of the amino terminus (residues 1 through 27) and the active-site cysteine cyanogen bromide peptide (residues 130 through 167) of this enzyme have been determined and compared with sequences of the enzyme from other sources. The importance of comparing phylogenetically related proteins is evident from the 87% identity found between these sequences in the enzyme from B. coagulans and Bacillus stearothermophilus, versus only 45% identity for all other known sequences. The marked sequence identity of the enzyme from the two Bacillus species drew attention to the variable region (residues 138 through 140a) which is exposed to the exterior of the quaternary structure of this enzyme. Based on the reported crystallographic structures of the enzyme from lobster muscle and B. stearothermophilus and space-filling models of the variable region, the segment Asp-Pro-Lys-Ala in B. stearothermophilus should be more thermostable than the analogous sequence, Asp-Ala-Ala-Asn, from B. coagulans. In addition, the space-filling models suggested that the spatial relationship of an amino acid side chain and its potential for close packing and interactions with neighboring side chains may be more important than the type of amino acid substituted.