Solvent effects on methyl transfer reactions. 2. The reaction of amines with trimethylsulfonium salts.

The reaction of ammonia and pyridine with trimethylsulfonium ion has been studied in gas phase and solution. Density functional theory at the B3LYP/6-31+G level was used to describe the energy changes along the reaction coordinate in the gas phase, and the self-consistent isodensity polarizable continuum model (SCI-PCM) was used to calculate the effect of cyclohexane and dimethyl sulfoxide as the solvent on the energy changes. The effect of water as the solvent was studied using the Monte Carlo free energy perturbation method. The reaction with both ammonia and pyridine follows a similar rather convoluted path in gas phase, with the formation of several reaction complexes before and after the formation of the transition state. All the species found in gas phase persist in cyclohexane, yielding a reaction path very similar to that in gas phase but with significant differences in the relative energy of the critical points. In DMSO, the energy profile is greatly simplified by the disappearance of several of the species found in gas phase and in cyclohexane. The activation free energy increases with the polarity of the solvent in both reactions. Increasing the polarity of the solvent also increases the exothermicity of the reaction of trimethylsulfonium ion with ammonia and reduces it in the reaction with pyridine. In water, the free energy profile follows the same trend as found for DMSO, and free energy of activation is calculated to be larger by about 2-3 kcal/mol. This is in good agreement with an experimental measurement of the effect of solvent on the rate of reaction.

An hPer2 phosphorylation site mutation in familial advanced sleep phase syndrome.

Familial advanced sleep phase syndrome (FASPS) is an autosomal dominant circadian rhythm variant; affected individuals are "morning larks" with a 4-hour advance of the sleep, temperature, and melatonin rhythms. Here we report localization of the FASPS gene near the telomere of chromosome 2q. A strong candidate gene (hPer2), a human homolog of the period gene in Drosophila, maps to the same locus. Affected individuals have a serine to glycine mutation within the casein kinase Iepsilon (CKIepsilon) binding region of hPER2, which causes hypophosphorylation by CKIepsilon in vitro. Thus, a variant in human sleep behavior can be attributed to a missense mutation in a clock component, hPER2, which alters the circadian period.

Uncoupling proteins 2 and 3 interact with members of the 14.3.3 family.

Uncoupling proteins (UCPs) are members of the superfamily of the mitochondrial anion carrier proteins (MATP). Localized in the inner membrane of the organelle, they are postulated to be regulators of mitochondrial uncoupling. UCP2 and 3 may play an important role in the regulation of thermogenesis and, thus, on the resting metabolic rate in humans. To identify interacting proteins that may be involved in the regulation of the activity of UCPs, the yeast two-hybrid system was applied. Segments of hUCP2 containing the hydrophilic loops facing the intermembrane space, or combinations of these, were used to screen an adipocyte activation domain (AD) fusion library. The 14.3.3 protein isoforms theta, beta, zeta were identified as possible interacting partners of hUCP2. Screening of a human skeletal muscle AD fusion library, on the other hand, yielded several clones all of them encoding the gamma isoform of the 14.3.3 family. Mapping experiments further revealed that all these 14.3.3 proteins interact specifically with the C-terminal intermembrane space domain of both hUCP2 and hUCP3 whereas no interactions could be detected with the C-terminal part of hUCP1. Direct interaction between UCP3 and 14.3.3 theta could be demonstrated after in vitro translation by coimmunoprecipitation. When coexpressed in a heterologous yeast system, 14.3.3 proteins potentiated the inhibitory effect of UCP3 overexpression on cell growth. These findings suggest that 14.3.3 proteins could be involved in the targeting of UCPs to the mitochondria.

Recombinant human uncoupling protein-3 increases thermogenesis in yeast cells.

The long form of human uncoupling protein-3 (hUCP3L) is highly homologous to thermogenin (UCPI), the uncoupling protein of brown fat mitochondria, but is expressed predominantly in skeletal muscle. Its putative role is to regulate the coupling efficiency of oxidative phosphorylation and thus thermogenesis in skeletal muscle, a major thermogenic tissue in higher mammals. To study the functional relevance of hUCP3L, the protein was expressed in yeast cells under the control of the galactose promoter. Expression of hUCP3L induced a series of phenotype changes in the yeast cells. The cellular growth and the mitochondrial membrane potential were both diminished. The portion of cellular respiration coupled to oxidative phosphorylation decreased from 57% to 11% (P<0.001) and the cellular heat production, as measured by direct microcalorimetry, was increased by 33.3 +/- 3.2% (P<0.001) after induction of UCP3L. These observations demonstrate for the first time the intrinsic thermogenic properties of hUCP3L in intact cells.

Properties of the human long and short isoforms of the uncoupling protein-3 expressed in yeast cells.

Two splice variants of the human uncoupling protein-3 (UCP3L and UCP3S) are highly expressed in skeletal muscle. The properties of UCP3L and S have been compared to those of UCP1 in a heterologous yeast expression system under the control of the galactose promoter. Both UCP3 isoforms were found to strongly impair the coupling efficiency of respiring cells thus resulting in increased thermogenesis. The uncoupling properties of both UCP3L and S could be clearly demonstrated also in isolated yeast mitochondria both in terms of coupled respiration and in the capacity to polarize the inner membrane in conditions of limited substrate availability. Contrary to what was observed with mitochondria containing UCP1, millimolar GDP and ATP had little if any effect on the uncoupling activity of UCP3. A very marked uncoupling of whole cells and isolated mitochondria was observed at very low expression levels of UCP3S indicating that the short isoform is more active than the long one.

Catalytic triad of microsomal epoxide hydrolase: replacement of Glu404 with Asp leads to a strongly increased turnover rate.

Microsomal epoxide hydrolase (mEH) belongs to the superfamily of alpha/beta-hydrolase fold enzymes. A catalytic triad in the active centre of the enzyme hydrolyses the substrate molecules in a two-step reaction via the intermediate formation of an enzyme-substrate ester. Here we show that the mEH catalytic triad is composed of Asp226, Glu404 and His431. Replacing either of these residues with non-functional amino acids results in a complete loss of activity of the enzyme recombinantly expressed in Saccharomyces cerevisiae. For Glu404 and His431 mutants, their structural integrity was demonstrated by their retained ability to form the substrate ester intermediate, indicating that the lack of enzymic activity is due to an indispensable function of either residue in the hydrolytic step of the enzymic reaction. The role of Asp226 as the catalytic nucleophile driving the formation of the ester intermediate was substantiated by the isolation of a peptide fraction carrying the 14C-labelled substrate after cleavage of the ester intermediate with cyanogen bromide. Sequence analysis revealed that one of the two peptides within this sample harboured Asp226. Surprisingly, the replacement of Glu404 with Asp greatly increased the Vmax of the enzyme with styrene 7,8-oxide (23-fold) and 9, 10-epoxystearic acid (39-fold). The increase in Vmax was paralleled by an increase in Km with both substrates, in line with a selective enhancement of the second, rate-limiting step of the enzymic reaction. Owing to its enhanced catalytic properties, the Glu404-->Asp mutant might represent a versatile tool for the enantioselective bio-organic synthesis of chiral fine chemicals. The question of why all native mEHs analysed so far have a Glu in place of the acidic charge relay residue is discussed.

Experiences in HCV-NAT screening prior to releasing cellular components by the German Red Cross Blood Transfusion Service of Baden-Württemberg.

In this report we present the accumulated data on nucleic acid testing (NAT) for hepatitis C virus (HCV) RNA of blood donations by the Blood Transfusion Service of Baden-Württemberg in the period between March 1997 and March 1999. An extra barcoded blood sample was collected from each donor. Samples were tested by NAT in mini-pools of maximally 96 samples. First-time and repeat donors were tested separately. RT/HCV-PCR was performed with the COBAS HCV Amplicortrade mark, versions 1.0 and 2.0 from Roche Diagnostic Systems. Many modifications have been introduced to the original protocol since the implementation of NAT screening aiming at an increase in the sensitivity and specificity of the assay. NAT positive pools containing serologically positive samples were detected. Initially, reactive pools were identified that could not be confirmed by secondary pooling and single testing procedures. So far, no serologically negative but NAT positive sample has been found.

Visualization of a covalent intermediate between microsomal epoxide hydrolase, but not cholesterol epoxide hydrolase, and their substrates.

Mammalian soluble and microsomal epoxide hydrolases have been proposed to belong to the family of alpha/beta-hydrolase-fold enzymes. These enzymes hydrolyse their substrates by a catalytic triad, with the first step of the enzymatic reaction being the formation of a covalent enzyme-substrate ester. In the present paper, we describe the direct visualization of the ester formation between rat microsomal epoxide hydrolase and its substrate. Microsomal epoxide hydrolase was precipitated with acetone after brief incubation with [1-(14)C]epoxystearic acid. After denaturing SDS gel electrophoresis the protein-bound radioactivity was detected by fluorography. Pure epoxide hydrolase and crude microsomes showed a single radioactive signal of the expected molecular mass that could be suppressed by inclusion of the competitive inhibitor 1,1,1-trichloropropene oxide in the incubation mixture. In a similar manner, 4-fluorochalcone-oxide-sensitive binding of epoxystearic acid to rat soluble epoxide hydrolase could be demonstrated in rat liver cytosol. Under similar conditions, no covalent binding of [26-(14)C]cholesterol-5alpha,6alpha-epoxide to microsomal proteins or solubilized fractions tenfold enriched in cholesterol epoxide hydrolase activity could be observed. Our data provide definitive proof for the formation of an enzyme-substrate-ester intermediate formed in the course of epoxide hydrolysis by microsomal epoxide hydrolase, show no formation of a covalent intermediate between cholesterol epoxide hydrolase and its substrate under the same conditions as those under which an intermediate was shown for both microsomal and soluble epoxide hydrolases and therefore indicate that the cholesterol epoxide hydrolase apparently does not act by a similar mechanism and is probably not structurally related to microsomal and soluble epoxide hydrolases.

The 5-lipoxygenase inhibitor zileuton blocks antigen-induced late airway responses, inflammation and airway hyperresponsiveness in allergic sheep.

Leukotrienes are thought to be involved in allergen-induced airway responses. To test this hypothesis we used a newly described 5-lipoxygenase inhibitor, zileuton, and examined its effect on antigen-induced early and late bronchial responses, airway inflammation and airway hyperresponsiveness in allergic sheep. Early and late responses were determined by measuring specific lung resistance (SRL) before and serially for 8 h after antigen challenge. Airway inflammation was assessed by bronchoalveolar lavage performed before, 8 h after and 24 h after antigen challenge. Airway responsiveness was measured before and 24 h after challenge by determining the dose of inhaled carbachol that caused a 400% increase in SRL (PD400%). The sheep (n = 8) were challenged with Ascaris suum antigen once after vehicle treatment (methylcellulose) and once after treatment with zileuton (10 mg/kg in methylcellulose, p.o.) given 2 h before antigen challenge. Trials were separated by at least 21 days. Zileuton had no effect on the early bronchoconstrictor response to antigen but the drug inhibited the late bronchial response by 55% (P less than 0.05). Unlike the control trial, there was no significant increase in bronchoalveolar lavage eosinophils at 8 h post challenge in the zileuton-treated sheep. Furthermore, zileuton treatment blocked (P less than 0.05) the airway hyperresponsiveness seen 24 h after challenge. Ex vivo formation of leukotriene B4 was inhibited over several hours after a single oral dose of zileuton, indicating that the compound was acting as a 5-lipoxygenase inhibitor in vivo. These results suggest that 5-lipoxygenase metabolites contribute to allergen-induced late responses, airway inflammation and airway hyperresponsiveness in this animal model of asthma.

Lysosomal proteinases as putative diagnostic tools in human neuropathology: Alzheimer disease (AD) and schizophrenia.

The cathepsin B, D and L were studied by immunohistochemical techniques in the human postmortem brain. The enzyme were primarily localized in neurons. Makroglial cells were seldom immunostained. It is shown that cathepsins B and D frequently occur in neuritic plaques of Alzheimer victims, thereby raising the question, whether or not cathepsin immunohistochemistry is a useful tool in the diagnosis of this disease. Furthermore, we identified certain glial cells to be immunoreactive for cathepsins in schizophrenics.

[1st animal experimental results with Bio-Vitroceramic implantations]. / Erste tierexperimentelle Ergebnisse mit Bio-Vitrokeramik-Implantaten.

In the framework of an expensive research project, the author made animal experiments to compare the bio-active behaviour of bio-vitroceramic implants with that of implants currently used. After experiments for more than a year, the author presents his first scanning electron microscopical findings that are indicative of direct binding of the implant to the bone.