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At least 775 records · Page 43Linked to original sources
PubMed1996

Quantitative structure-activity relationship study of fibrinogen inhibitors, [[4-(4-amidinophenoxy)butanoyl]aspartyl]valine (FK633) derivatives, using a novel hydrophobic descriptor.

We recently reported a novel hydrophobic descriptor for quantitative structure-activity relationship (QSAR) studies, the logarithm of the partition coefficient micelle/water (log Pmw), which is easily determined by a HPLC system and is thought to be a descriptor for a compound's affinity to a biomembrane. We carried out QSAR studies using log Pmw on the antiplatelet activities of novel fibrinogen inhibitors, [[4-(4-amidinophenoxy)butanoyl]aspartyl]valine (FK633) derivatives, which resulted in a quadratic curve with a good correlation coefficient (n = 12, s = 0.368, F = 14.1**, r = 0.871), indicating that a suitable membrane affinity of the fibrinogen inhibitors is vital for their inhibitory activities. QSAR studies using STERIMOL parameters and/or CLOGP values were unsuccessful.

Dipeptides↗
PubMed2006

Computational study of matrix-peptide interactions in MALDI mass spectrometry: Interactions of 2,5- and 3,5-dihydroxybenzoic acid with the tripeptide valine-proline-leucine.

The mechanism of matrix-to-analyte proton transfer in matrix-assisted laser desorption and ionization mass spectrometry (MALDI-MS) has been investigated computationally by modeling the matrix-analyte interaction of potential MALDI matrixes such as 2,5-dihydroxybenzoic acid (2,5-DHB) and 3,5-DHB with the tripeptide valine-proline-leucine (VPL). A combination of molecular dynamics/simulated annealing calculations followed by density functional theory geometry optimization using a reasonably large basis set has been done on a large number of clusters in an attempt to study the ionization energy of each matrix in the cluster environment and the intracluster proton transfer from the matrix to the tripeptide. The calculations show a substantial reduction in the IP for both matrixes in their cluster environments. In the 2,5-system, proton transfer can sometimes occur in the neutral clusters (preformed ions), whereas proton transfer in the cationic clusters, which is actually a double proton transfer, is spontaneous and exoergic. Even though it is more acidic from a thermodynamic perspective, the radical cation of 3,5-DHB is a less efficient proton donor to VPL. The thermodynamics of proton transfer in the cationic clusters is discussed in detail.

Computational Biology↗
PubMed2000

A valine-derived lithiated 3-methylthiomethyl-1,3-oxazolidin-2-one for enantioselective nucleophilic hydroxymethylation, formylation, and alkoxycarbonylation of aldehydes

The 3-methylthiomethyl-4-isopropyl-5,5-diphenyl-1,3-oxazolidin-2-one (I, prepared in three steps from Boc-valine ester) is lithiated and added to aldehydes, with protecting in situ trapping of the primary adducts, to give the N,S-acetal derivatives II of 2-hydroxy aldehydes in high yields and diastereoselectivities. Cleavage (with ready recovery of the oxazolidinone auxiliary) is possible, to afford, for instance, enantiopure 1,2-diols, selectively protected (OBn, OMOM, OTBS) in the 2-position.

Journal Article↗
PubMed1997

Imprinting effects of proline containing dipeptides (proline-glycine, proline-leucine, proline-valine and their retro variants) in tetrahymena. Evolutionary conclusions.

Proline-glycine, proline-leucine and proline-valine dipeptides and their retro variants were used in the experiments to study the effects of pretreatment (imprinting) in Tetrahymena, by investigating fluorescein isothiocyanate (FITC)-conjugated peptide binding. The protozoan organism could differentiate between the proline-dipeptides containing different partner amino-acids and between the dipeptides having the amino acids in reversed positions. The effect of imprinting was positive or negative and this was dependent on the type of the partner amino acid and on its position. Pro-Gly and Pro-Leu induced positive imprinting (elevated FITC-dipeptide binding) and Pro-Val induced negative imprinting (decrease of FITC-peptide binding). There was positive imprinting induction in two cases for the retro FITC-peptide and in one case for the FITC-conjugate of the imprinter peptide itself. The highest positive imprinting (almost 60% increase) was induced by Pro-Gly for FITC-Gly-Pro. Considering earlier--chemotaxis--experiments, the results of the present--binding--studies run parallel with the physiological effects. The experiments call attention to the sharp differentiating ability of small peptides at a unicellular level, that could have some role in the selection of molecules for hormone formation, during evolution.

Animals↗
PubMed1993

Delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase, the multienzyme integrating the four primary reactions in beta-lactam biosynthesis, as a model peptide synthetase.

ACV synthetase forms the tripeptide precursor of penicillins and cephalosporins from alpha-aminoadipate, cysteine, and valine. Catalytic sites for substrate carboxyl activation as adenylates, peptide bond formations, epimerization and release of the tripeptide-thioester are integrated in multifunctional enzymes of 405 to 425 kD. These have been characterized from several pro- and eukaryotic beta-lactam producers. Implications of these results for the thio-template mechanism of peptide formation are discussed, as well as the use of this multienzyme as a model system for enzymatic peptide synthesis.

Amino Acid Sequence↗
PubMed2004

Synthesis of (2S,3R)-[3',3',3'-2H3]-valine and (2S,3S)-4-fluorovaline.

A new synthesis of (2S,3R)-[3',3',3'-2H3]-valine has been completed and (2S,3S)-4-fluorovaline has been synthesised for the first time. Both compounds have been prepared by routes involving stereoselective addition to the (S)-pyroglutamate derivative and are available for studies in several areas of bio-organic chemistry.

Journal Article↗
PubMed1979

Cell-free conversion of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine into an antibiotic with the properties of isopenicillin N in Cephalosporium acremonium.

Cell-free extracts of antibiotic-negative mutants of Cephalosporium acremonium converted delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (LLD-tripeptide) into an antibiotic that was destroyed by penicillinase. The enzymic activity of the extracts was destroyed by boiling, but was not inhibited by cycloheximide. LLL-Tripeptide was totally inactive as substrate. The product resembled isopenicillin N, but not penicillin N, in its antibacterial spectrum. We propose that isopenicillin N is the first product of cyclization of LLD-tripeptide.

Acremonium↗
PubMed1987

Sources of propionate for the biogenesis of ethyl-branched insect juvenile hormones: Role of isoleucine and valine.

Corpora allata from adult female Manduca sexta biosynthesize the sesquiterpenoid juvenile hormone (JH) III and the unusual ethyl-branched homologue JH II in vitro. We maintained corpora allata in medium 199 using [methyl-(3)H]methionine as the source of the JH methyl ester moiety and as a mass marker. This allowed measurement of the relative contributions of (14)C-labeled precursors to the biogenesis of JH II and III carbon skeletons. We showed efficient incorporation of a propionate equivalent, from isoleucine or valine catabolism, into the ethyl-branched portion of JH II, using double-label liquid scintillation counting of isolated JHs and gas chromatography/mass spectrometry with selected ion monitoring of JH deuteromethoxyhydrin derivatives. Methionine was a poor source of propionate for JH II biosynthesis, while glucose, succinate, threonine, and beta-alanine did not contribute propionate at all. Leucine, isoleucine, and glucose incorporated into JH III and the acetate-derived portion of JH II.

Journal Article↗
PubMed1991

Pelizaeus-Merzbacher disease: a valine to phenylalanine point mutation in a putative extracellular loop of myelin proteolipid.

In the central nervous system, myelin proteolipid protein isoforms (PLP and DM20) play an essential structural role in myelination. It has been shown in several species that myelination is impaired by molecular defects resulting from single base mutations in the PLP gene. We have used DNA amplification by polymerase chain reaction to study the PLP gene coding regions from 17 patients in 15 unrelated families with similar Pelizaeus-Merzbacher phenotype. In one case amplification of peripheral nerve PLP/DM20 cDNAs revealed that a silent T----C transition was unrelated to the disease. In one family a nonsilent mutation was identified that leads to a phenylalanine substitution for valine-218 in PLP/DM20 proteins. We investigated the inheritance of the mutant allele in 19 subjects of this four-generation family and found a strict cosegregation of the Phe218 substitution with transmission and expression of the disease. The effect of the Val218----Phe mutation is discussed in the frame of a recently suggested topological model of PLP/DM20, according to which Val218 is part of an extracellular loop that connects the last two of four membrane-spanning alpha-helices.

Animals↗
PubMed1997

Analysis of the quaternary structure, substrate specificity, and catalytic mechanism of valine dehydrogenase.

The solution of the three-dimensional structure of Bacillus sphaericus leucine dehydrogenase has enabled us to undertake a homology-based modeling exercise on the sequence differences between the families of leucine (LeuDH) and valine (ValDH) dehydrogenases. This analysis indicates that the secondary structure elements in the core of the two domains of a single subunit of these enzymes are conserved, as are residues directly implicated in the recognition of the nucleotide cofactor and in catalysis. Comparison of the sequences indicates that the residues in the pocket accommodating the side chain of the amino acid substrate are conserved between these two enzymes, suggesting that the small differences in specificity arise from minor changes in molecular structure, possibly associated with shifts of the main chain rather than mutation of residues in the pocket itself. While B. sphaericus LeuDH is an octamer, both Streptomyces cinnamonensis and Streptomyces coelicolor ValDHs are dimers. The differences in quaternary structure can be understood in terms of the deletion in the latter of a C-terminal loop, which forms important interactions around the four-fold axis in LeuDH.

Amino Acid Oxidoreductases↗
PubMed1998

Substitution of valine for histidine 265 in carbon monoxide dehydrogenase from Rhodospirillum rubrum affects activity and spectroscopic states.

In carbon monoxide dehydrogenase (CODH) from Rhodospirillum rubrum, histidine 265 was replaced with valine by site-directed mutagenesis of the cooS gene. The altered form of CODH (H265V) had a low nickel content and a dramatically reduced level of catalytic activity. Although treatment with NiCl2 and CoCl2 increased the activity of H265V CODH by severalfold, activity levels remained more than 1000-fold lower than that of wild-type CODH. Histidine 265 was not essential for the formation and stability of the Fe4S4 clusters. The Km and KD for CO as well as the KD for cyanide were relatively unchanged as a result of the amino acid substitution in CODH. The time-dependent reduction of the [Fe4S4]2+ clusters by CO occurred on a time scale of hours, suggesting that, as a consequence of the mutation, a rate-limiting step had been introduced prior to the transfer of electrons from CO to the cubanes in centers B and C. EPR spectra of H265V CODH lacked the gav = 1.86 and gav = 1.87 signals characteristic of reduced forms of the active site (center C) of wild-type CODH. This indicates that the electronic properties of center C have been modified possibly by the disruption or alteration of the ligand-mediated interaction between the nickel site and Fe4S4 chromophore.

Aldehyde Oxidoreductases↗
PubMed2001

Control of prostaglandin stereochemistry at the 15-carbon by cyclooxygenases-1 and -2. A critical role for serine 530 and valine 349.

Prostaglandin synthesis by cyclooxygenases-1 and -2 (COX-1 and COX-2) involves an initial oxygenation of arachidonic acid at C-11, followed by endoperoxide and cyclopentane ring formation, and then a second reaction with molecular oxygen in the S configuration at C-15. The resulting 15S-hydroxyl group of prostaglandins is crucial for their bioactivity. Using human COX-1 and human and murine COX-2, we have identified two amino acids located in the oxygenase active site that control the stereochemistry at C-15. The most crucial determinant is Ser-530, the residue that is acetylated by aspirin. In COX-2, site-directed mutagenesis of Ser-530 to methionine, threonine, or valine produced highly active enzymes that formed 82-95% 15R-configuration prostaglandins; these have the opposite stereochemistry at C-15 to the natural products. In COX-1, the corresponding Ser-530 mutations inactivated the enzyme. The second residue, Val-349, exerts a more subtle influence. When Val-349 was replaced by isoleucine, the mutant COX-1 and COX-2 enzymes formed 41 and 65% 15R-prostaglandins, respectively. This change was highly specific for isoleucine, as mutations of Val-349 to alanine, leucine, asparagine, or threonine did not alter or only slightly altered (< or =13%) the S-configuration at C-15. These results establish a previously unrecognized role for Ser-530 and Val-349 in maintaining the correct S stereochemistry of the carbon-15 hydroxyl group during prostaglandin synthesis. The findings may also explain the absolute conservation of Ser-530, the target of aspirin, throughout the families of cyclooxygenase enzymes.

Animals↗
PubMed2003

(19)F NMR studies of the leucine-isoleucine-valine binding protein: evidence that a closed conformation exists in solution.

The leucine-isoleucine-valine binding protein (LIV) found in the periplasmic space of E. coli has been used as a structural model for a number of neuronal receptors. This "venus fly trap" type protein has been characterized by crystallography in only the open form. Herein we have labeled LIV with 5-fluorotryptophan (5F-Trp) and difluoromethionine (DFM) in order to explore the structural dynamics of this protein and the application of DFM as a potential (19)F NMR structural probe for this family of proteins. Based on mass spectrometric analysis of the protein overproduced in the presence of DFM, approximately 30% of the five LIV methionine residues were randomly substituted with the fluorinated analog. Urea denaturation experiments imply a slight decrease in protein stability when DFM is incorporated into LIV. However, the fluorinated methionine did not alter leucine-binding activity upon its incorporation into the protein. Binding of L-leucine stabilizes both the unlabeled and DFM-labeled LIV, and induces the protein to adopt a three-state unfolding model in place of the two-state process observed for the free protein. The (19)F NMR spectrum of DFM-labeled LIV gave distinct resonances for the five Met residues found in LIV. 5F-Trp labeled LIV gave a well resolved spectrum for the three Trp residues. Trp to Phe mutants defined the resonances in the spectrum. The distinct narrowing in line width of the resonances when ligand was added identified the closed form of the protein.

Bacterial Proteins↗
PubMed1999

Inherited prion disease with an alanine to valine mutation at codon 117 in the prion protein gene.

A large English family with autosomal dominant segregation of presenile dementia, ataxia and other neuropsychiatric features is described. Diagnoses of demyelinating disease, Alzheimer's disease, Creutzfeldt-Jakob disease (CJD) and Gerstmann-Sträussler-Scheinker syndrome have been attributed to particular individuals at different times. An Irish family, likely to be part of the same kindred, is also described, in which diagnoses of multiple sclerosis, dementia, corticobasal degeneration and new variant CJD have been considered in affected individuals. Molecular genetic studies have enabled the classification of this disease at the molecular level as one of the group of inherited prion diseases, with the substitution of valine for alanine at codon 117 of the prion protein gene (PRNP). Only three other kindreds have been described world-wide with this mutation and only limited phenotypic information has been reported. Here we describe the phenotypic spectrum of inherited prion disease (PrPA117V). The diversity of phenotypic expression seen in this kindred emphasizes the logic of molecular classification of the inherited prion diseases rather than classification by specific clinicopathological syndrome. Indeed, inherited prion disease should be excluded by PRNP analysis in any individual presenting with atypical presenile dementia or neuropsychiatric features and ataxia, including suspected cases of new variant CJD.

Adult↗
PubMed1982

Nucleotide sequence of valine tRNA mo5UAC from bacillus subtilis.

A valine tRNA was purified from Bacillus subtilis W168 by a combined use of several column chromatographic systems. The nucleotide sequence was determined to be pG-G-A-G-G-A-U-U-A-G-C-U-C-A-G-C-D-G-G-G-A-G-A-G-C-A-U-C--G-C-C-U-mo5U-A-C-m6-A -A-G-C-A-G-A-G-G-m7G-U-C-G-G-C-G-G-T-psi-C-G-A-G-C-C-C-G-U-C-A-U-C-C-U-C-C-A-C- C-AOH with the main use of of non-labeled tRNA and with the subsidiary use of [32P]-post-labeled sample. This tRNA contains 5-methoxy-uridine (mo5U) at the wobble position of the anticodon. A binding experiment of valyl-tRNA to ribosome revealed that mo5U is recognized by A and G, and fairly well by U.

Bacillus subtilis↗
PubMedDate not supplied

The 1998 Moyer Award. Characteristics of thrombospondin-1 and its cysteine-serine-valine-threonine-cysteine-glycine receptor in burn wounds.

Thrombospondin-1 (TSP-1), an adhesive glycoprotein, plays an important role in platelet adhesion, inflammation, cell-to-cell interaction, and angiogenesis. TSP-1 is expressed by endothelial cells, fibroblasts, and macrophages. TSP-1's unique cysteine-serine-valine-threonine-cysteine-glycine (CSVTCG) specific receptor plays an important role in the binding and modulation of cellular adhesion and invasion. This article histologically and quantitatively evaluates TSP-1 and its CSVTCG receptor in adult burn wounds over time. Tissue was obtained from burn wounds on several days and samples that were 5 microns thick were placed on slides. Expression of TSP-1 and its CSVTCG receptor were evaluated immunohistochemically and quantitated by computer image analysis in units of absorbance. Immunoglobin G (IgG) (negative) controls were performed and subtracted from the TSP-1 sample to eliminate background absorbance readings. Serum (negative) control was used for the CSVTCG receptor. Platelet concentrates were used as the positive control. A quantitative examination of the results yielded the following information, expressed as absorbance +/- standard error of the mean: TSP-1: day 1, 62.0 +/- 10.13; day 3, 76.2 +/- 6.90; day 5, 36.0 +/- 3.96; day 7, 60.4 +/- 5.67; and day 9, 29.5 +/- 2.91. TSP-1 displays an early peak, followed by a steep decrease over the time period studied. The readings for the CSVTCG receptor are as follows: day 1, 33.8 +/- 1.87; day 3, 34.5 +/- 5.39; day 7, 39.1 +/- 1.93; day 21, 39.1 +/- 1.93; day 28, 34.8 +/- 3.67. In contrast, the CVSTCG receptor continues to be present in the wound over time. Histologic findings are reported, and photographs and a histopathologic analysis are included. The information presented in this article leads to the conclusion that temporal and histologic differences exist in the localization and expression of TSP-1 and its CSVTCG receptor. TSP-1 is up-regulated in injured tissues immediately after the injury; it is rapidly down-regulated as the tissue heals. In contrast, the levels of the CSVTCG receptor remain relatively constant during the healing process. These data are consistent with TSP-1's known role in cell-to-cell interaction, including the modulation of the growth factor and protease activity.

Adult↗
PubMed1986

Glucose regulation of cephamycin biosynthesis in Streptomyces lactamdurans is exerted on the formation of alpha-aminoadipyl-cysteinyl-valine and deacetoxycephalosporin C synthase.

Glucose exerted a concentration-dependent negative regulation on the biosynthesis of cephamycin C by Streptomyces lactamdurans. Formation of the cephamycin precursor delta(alpha-aminoadipyl)-cysteinyl-valine was greatly decreased by excess glucose. The ring-expanding enzyme deacetoxycephalosporin C synthase was strongly repressed by glucose in vivo. Isopenicillin N synthase (cyclase) and isopenicillin N epimerase were not repressed by glucose. However, the activity of isopenicillin N synthase was inhibited in vitro by glucose 6-phosphate, and the activity of deacetoxycephalosporin C synthase was inhibited by inorganic phosphate, glucose 6-phosphate, fructose 2,6-diphosphate and fructose 1,6-diphosphate. The intracellular cAMP content decreased as growth proceeded and remained lower in glucose-supplemented cells than in control cultures. cAMP did not seem to be involved in glucose control of cephamycin biosynthesis.

Amino Acid Isomerases↗