Do the major human glutathione S-transferases have fatty acid ethyl ester synthase activity?

Two fatty acid ethyl ester (FAEE) synthase isoenzymes purified from human myocardium were reported to be glutathione S-transferases (GST) [(1989) Proc. Natl. Acad. Sci. USA 86, 4470-4473; and (1989) J. Clin. Invest. 84, 1942-1946]. In the present study, the FAEE synthase activity of several purified and well characterized human GSTs were examined with ethanol and [14C]oleic acid as substrates. Three isoenzymes, GST1, GST2 and GST3 which are members of the evolutionary classes mu, alpha, and pi, respectively, were studied and failed to show any significant synthesis of FAEE after 45 min incubation at 37 degrees C. FAEE synthase activity and GST3 activity in human placental extracts can be readily separated by ion exchange chromatography on DEAE cellulose. Thus the results show that FAEE synthase activity is not a feature of the major GSTs found in human tissues. The two FAEE synthase isoenzymes isolated by Bora et al. may have been co-purified with GST isoenzymes or these FAEE synthases may be members of the GST super family that have low specific activity in conventional GST assays and have not been previously described.     

Kinetic investigation of a solvent-free, chemoenzymatic reaction sequence towards enantioselective synthesis of a β-amino acid ester

A solvent-free, chemoenzymatic reaction sequence for the enantioselective synthesis of β-amino acid esters has been kinetically and thermodynamically characterized. The coupled sequence comprises a thermal aza-Michael addition of cheap starting materials and a lipase catalyzed aminolysis for the kinetic resolution of the racemic ester. Excellent ee values of >99% were obtained for the β-amino acid ester at 60% conversion. Kinetic constants for the aza-Michael addition were obtained by straightforward numerical integration of second-order rate equations and nonlinear fitting of the progress curves. A different strategy had to be devised for the biocatalytic reaction. Initially, a simplified Michaelis-Menten model including product inhibition was developed for the reaction running in THF as an organic solvent. Activity based parameters were used instead of concentrations in order to facilitate the transfer of the kinetic model to the solvent-free system. Observed solvent effects not accounted for by the use of thermodynamic activities were incorporated into the kinetic model. Enzyme deactivation was observed to depend on the ratio of the applied substrates and also included in the kinetic model. The developed simple model is in very good agreement with the experimental data and allows the simulation and optimization of the solvent-free process.     

Properties of [3H] ß-carboline-3-carboxylate ethyl ester binding to the benzodiazepine receptor

β-Carbolines are inhibitors of [³H] diazepam binding with the most potent inhibitor being β-carboline-3-carboxylate ethyl ester (β-CCE). In this report the binding of [³H] β-CCE to extensively washed rat forebrain membranes is characterized. [³H] ß-CCE binds with high affinity (K_D = 1.4 nM) to an apparently homogenous population of benzodiazepine receptor. The rank order of potency for inhibition of [³H] ß-CCE binding by different benzodiazepines is clonazepam > diazepam > chlordiazepoxide, which is similar to that observed for inhibition of [³H] diazepam binding. In marked contrast to [³H] diazepam, the binding of [³H] ß-CCE is not modulated by GABA since concentrations of GABA as high as 10^?3 M had no effect. [³H] ß-CCE is also less potent than [³H] diazepam in its interaction with the peripheral type kidney benzodiazepine receptor indicating that this ligand has a higher degree of specificity for the central brain type benzodiazepine receptor.     

Application of comparative proteome analysis to reveal influence of cultivation conditions on asymmetric bioreduction of β-keto ester by Saccharomyces cerevisiae

Industrial bakers' yeast strain Saccharomyces cerevisiae LH1 was selected for asymmetric reduction of ethyl benzoylacetate to (S)-ethyl 3-hydroxy-3-phenylpropionate. Higher reductive efficiency and higher cofactor availability were obtained with the alternation of cultivation condition (mainly growth medium). Compared to the bioreduction by yeast cells grown in malt extract (ME) medium, the concentration of substrate was increased 25-fold (up to 15.6 g/l) in the yeast peptone dextrose (YPD)-grown cells mediated bioreduction with 97.5% of enantioselective excess of (S)-product. The proteomic responses of S. cerevisiae LH1 cells to growth in aerobic batch cultures fed with either YPD or ME medium were examined and compared. Among the relative quantities of 550 protein spots in each gel, changes were shown in the expression level of 102 intracellular proteins when comparing YPD gel to ME gel. Most of the identified proteins were involved in energy metabolism and several cellular molecular biosynthetic pathway and catabolism. For YPD-grown yeast cells, not only enzymes involved in nicotinamide adenine dinucleotide phosphate regeneration, especially 6-phosphogluconate dehydrogenase, but also alcohol dehydrogenase 1 and D: -arabinose 1-dehydrogenase which had been demonstrated activity toward ethyl benzoylacetate to (S)-hydroxy ester were significantly upregulated. These changes provided us insight in the way the yeast cells adapted to a change in cultivation medium and regulated its catalytic efficiency in the bioreduction.     

Vitamin K1 dependent carboxylase: β-Carboxylation of t-butyloxycarbonylaspartic acid α-benzyl ester

Rat liver microsomes solubilized by Triton X-100 catalyze the vitamin K₁ dependent incorporation of carbon-14 from [¹⁴C]NaHCO₃ into t-butyloxycarbonylaspartic acid α-benzyl ester. High voltage electrophoresis of the alkaline hydrolysate of the products of this reaction demonstrates the presence of a labelled species (A) whose electrophoretic mobility is identical to that of β-carboxyaspartic acid. High voltage electrophoresis of the acid-treated products reveals the disappearance of A and the appearance of a labelled species whose electrophoretic mobility is identical to that of aspartic acid. These experiments provide unequivocal evidence for the vitamin K₁ dependent β-carboxylation of an aspartic acid side chain, and they constitute the first report of such an enzymatic activity in microsomes.     

Proteases as catalysts of enantioselective α-amino ester hydrolysis: 2. Pronase-catalysed hydrolysis of tryptophan methyl ester

The influence of pH, temperature, EDTA and metal ions on the rate of hydrolysis of methyl esters of d- and l-tryptophan by pronase from Streptomyces griseus has been studied. pH, Ca²⁺ and Co²⁺ ions have different effects on the hydrolysis of d- and l-substrates, which permits the enantioselectivity of the reaction to be regulated. Maximum enantioselectivity was observed at pH 7 in the presence of 10^?3–10^?2m Co²⁺. The data obtained are compared with the literature data for the hydrolysis of other low molecular weight substrates by pronase. It is suggested that leucine aminopeptidase makes a considerable contribution to the observed esterase activity of pronase.     

Molecular docking and 3D-QSAR studies on β-phenylalanine derivatives as dipeptidyl peptidase IV inhibitors

Three-dimensional quantitative structure-activity relationship (3D-QSAR) and molecular docking studies were carried out to explore the binding of 73 inhibitors to dipeptidyl peptidase IV (DPP-IV), and to construct highly predictive 3D-QSAR models using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). The negative logarithm of IC₅₀ (pIC₅₀) was used as the biological activity in the 3D-QSAR study. The CoMFA model was developed by steric and electrostatic field methods, and leave-one-out cross-validated partial least squares analysis yielded a cross-validated value (r_cv² {\hbox{r}}_{{\rm{cv}}}^{\rm{2}} ) of 0.759. Three CoMSIA models developed by different combinations of steric, electrostatic, hydrophobic and hydrogen-bond fields yielded significant r_cv² {\hbox{r}}_{{\rm{cv}}}^{\rm{2}} values of 0.750, 0.708 and 0.694, respectively. The CoMFA and CoMSIA models were validated by a structurally diversified test set of 18 compounds. All of the test compounds were predicted accurately using these models. The mean and standard deviation of prediction errors were within 0.33 and 0.26 for all models. Analysis of CoMFA and CoMSIA contour maps helped identify the structural requirements of inhibitors, with implications for the design of the next generation of DPP-IV inhibitors for the treatment of type 2 diabetes.     

Enzymatic β-galactosidation of β-xylopyranosides

Summary The disaccharides formed by enzymatic transfer of the -D-galactopyranosyl residue fromo-nitrophenyl -d-galactopyranoside to -d-xylopyranosides have been identified. The influence of different factors on the yields of the disaccharides obtained was evaluated. Significant changes in selectivity were observed when -galactosidase fromE. coli was used instead of -galactosidase fromA. oryzae.     

γ-glutamylcysteine ethyl ester protects cerebral endothelial cells during injury and decreases blood-brain barrier permeability after experimental brain trauma

Oxidative stress is a pathway of injury that is common to almost all neurological conditions. Hence, methods to scavenge radicals have been extensively tested for neuroprotection. However, saving neurons alone may not be sufficient in treating CNS disease. In this study, we tested the cytoprotective actions of the glutathione precursor gamma-glutamylcysteine ethyl ester (GCEE) in brain endothelium. First, oxidative stress was induced in a human brain microvascular endothelial cell line by exposure to H(2)O(2). Addition of GCEE significantly reduced formation of reactive oxygen species, restored glutathione levels which were reduced in the presence of H(2)O(2), and decreased cell death during H(2)O(2)-mediated injury. Next, we asked whether GCEE can also protect brain endothelial cells against oxygen-glucose deprivation (OGD). As expected, OGD disrupted mitochondrial membrane potentials. GCEE was able to ameliorate these mitochondrial effects. Concomitantly, GCEE significantly decreased endothelial cell death after OGD. Lastly, our in vivo experiments using a mouse model of brain trauma show that post-trauma (10 min after controlled cortical impact) administration of GCEE by intraperitoneal injection results in a decrease in acute blood-brain barrier permeability. These data suggest that the beneficial effects of GCEE on brain endothelial cells and microvessels may contribute to its potential efficacy as a neuroprotective agent in traumatic brain injury.     

Possible Identity of β-Xylosidase and β-Glucosidase of Chaetomium trilaterale

The nature of the active site of Chaetomium trilaterale β-xylosidase catalyzing the hydrolysis of β-d-glucopyranoside and β-d-xylopyranoside was investigated by kinetic methods. On experiments with mixed substrates, such as phenyl β-d-xylopyranoside and phenyl β-d-glucopyranoside, the kinetic features agreed very closely with those features theoretically predicted for a single active site of the same enzyme catalyzing the hydrolysis of these two kinds of substrates.

Both the β-glucosidase and β-xylosidase activities were strongly inhibited by glucono-1,5-lactone and nojirimycin (5-amino-5-deoxy-d-glucopyranose). β-Xylosidase activity was inhibited non-competitively by the two inhibitors, but β-glucosidase activity was competitive. Methyl β-d-xylopyranoside, methyl β-d-glucopyranoside, 1-thiophenyl β-d-xylopyranoside, and 1-thiophenyl β-d-glucopyranoside poorly inhibited both activities. Methyl β-d-xylopyranoside inhibited the β-xylosidase activity competitively but the β-glucosidase activity was non-competitive, whereas methyl β-d-glucopyranoside inhibited the β-xylosidase activity non-competitively but the β-glucosidase activity was competitive. 1-Thiophenyl β-d-xylopyranoside and 1-thiophenyl β-d-glucopyranoside behaved as competitive inhibitors.

From these results, it was concluded that the β-xylosidase and β-glucosidase activities reside in one catalytic site, and this suggests that there might be two kinetically distinct binding sites in the active center of the same enzyme.     

Expression of the β-subunit of β-conglycinin in seeds of transgenic plants

Soybean (Glycine max (L.) Merr.) seeds contain the storage protein -conglycinin, encoded by a multigene family. -Conglycinin consists of three subunits; , , and . A genomic clone for a -subunit of -conglycinin has been characterized by restriction-enzyme mapping and hybrid selected in-vitro translation followed by immunoprecipitation. In order to determine the developmental regulation of this -subunit gene, its expression was studied in seeds of transgenic petunia (Petunia hybrida) and tobacco (Nicotiana tabacum L.) plants. The -subunit expressed in seeds of petunia and tobacco was recognized by anti--conglycinin serum at a relative molecular mass of 53 000, equivalent to that of the native protein. Separation of the petunia-seed proteins by isoelectric focusing followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis showed that multiple isoelectric forms of the -subunit were produced. There was approximately a twofold variation in the accumulation of the -subunit protein in the mature seeds of transgenic petunia plants, each containing a single -subunit gene. However, the level of protein accumulation in mature seeds and the amount of -subunit mRNA in developing seeds was not correlated. Accumulation of the -subunit protein in transgenic seeds was less than the -subunit protein that accumulated in transgenic petunia seeds containing a single -subunit gene and less than the amount of the -subunit in mature soybean seeds which contain 8–13 -subunit genes. In transgenic tobacco plants, the accumulation of the -subunit protein in seeds was generally well correlated with the number of genes that were incorporated in the different transformants.Abbreviations kb kilobase - kDa kilodalton - M_r relative molecular mass - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis     

Synthesis of β-Tubanol

Synthesis of β-tubanol (VIa) was achieved by the bromination of dihydro-β-tubanol acetate (VIIb) followed by dehydrobromination and the subsequent hydrolysis. 2,2-Dimethyl-5-hydroxy-chromanone as well as its derivatives (IV) and the corresponding chromanols (V) and chromans (VII) were also prepared.     

Prediction of β-Turns

Kohonen's self-organization model, a neural network model, is applied to predict the β-turns in proteins. There are 455 β-turn tetrapeptides and 3807 non-β-turn tetrapeptides in the training database. The rates of correct prediction for the 110 β-turn tetrapeptides and 30,229 non-β-turn tetrapeptides in the testing database are 81.8% and 90.7%, respectively. The high quality of prediction of neural network model implies that the residue-coupled effect along a polypeptide chain is important for the formation of reversal turns, such as β-turns, during the process of protein folding.     

Folding of β-Hairpins

Identification of the factors governing the formation of -structure independently of the rest of the protein is important for understanding the folding process of protein into a unique native structure. It has been shown that some -hairpins can fold autonomously into native-like structures, either in aqueous solution or in the presence of an organic co-solvent. Our aim is to review recent theoretical and experimental studies of folding of -structures.     

Prediction of β-Turns

Kohonen's self-organization model, a neural network model, is applied to predict the -turns in proteins. There are 455 -turn tetrapeptides and 3807 non--turn tetrapeptides in the training database. The rates of correct prediction for the 110 -turn tetrapeptides and 30,229 non--turn tetrapeptides in the testing database are 81.8% and 90.7%, respectively. The high quality of prediction of neural network model implies that the residue-coupled effect along a polypeptide chain is important for the formation of reversal turns, such as -turns, during the process of protein folding.