Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Imidazole catalysis of phenylalanyl transfer from phenylalanine adenylate anhydride to the hydroxyl groups of homopolyribonucleotides was investigated as a chemical model of the biochemical aminoacylation of tRNA. Imidazole catalyzed transfer of phenylalanine to poly(U) increases from pH 6.5 to 7.7 and decreases above pH 7.7. At pH 7.7 approximately 10% of the phenylalanyl residues are transferred to poly(U). At pH 7.1, transfer to poly(U) was five times as great as to poly(A) and transfer to a poly(A) poly(U) double helix was negligible. At pH 7.1 approximately 45 mole percent linkages to poly(U) were monomeric phenylalanine; the remainder of the linkages were peptides of phenylalanine. The number of linkages and their lability to base and neutral hydroxylamine indicates that phenylalanine and its peptides are attached as esters to the 2' hydroxyl groups throughout poly(U) and the 2' (3') hydroxyl groups at the terminus of poly(U). These results do model the contemporary process of aminoacyl transfer to tRNA and continue to suggest that a histidine residue is in the active site of aminoacyl-tRNA-synthetases.
 ...
PMID:Aminoacyl transfer from an adenylate anhydride to polyribonucleotides. 0 44

Methioninase of Pseudomonas putida was purified to homogeneity, as judged by polyacrylamide gel electrophoresis, with a specific activity 270-fold higher than that of the crude extract. 1. The purified enzyme had an S20,w of 8.37, a molecular weight of 160,000, and an isoelectric point of 5.6. 2. A break in the Arrhenius plot was observed at 40 degrees and the activation energies below and above this temperature were 15.5 and 2.97 kcal per mole, respectively. 3. In addition to L-methionine, various S-substituted derivatives of homocysteine and cysteine could serve as substrates. D-Methionine, 2-oxo-4-methylthiobutanoate, and related non sulfur-containing amino acids were inert. Equimolar formation of alpha-ketobutyrate and CH3SH was observed with methionine as a substrate. 4. In addition to the protein peak at 278 nm, two absorption maxima were observed at 345 and 430 nm at pH 7.5. Hydroxylamine removed the enzyme-bound pyridoxal phosphate, resulting in almost complete resolution with the concomitant disappearance of both peaks. Reconstruction of the treated enzyme could be achieved by addition of the cofactor; the Km value was calculated to be 0.37 muM. 5. The reported purified enzyme should be designated as L-methionine methanethiollyase (deaminating).
 ...
PMID:Purification and characterization of methioninase from Pseudomonas putida. 0 40

Inactivation of yeast phosphoglyceromutase (tetramer) with 1,2-cyclohexanedione correlates with the modification of six arginyl residues per mole of the enzyme. Protection experiments using 3-phosphoglycerate suggest that four arginyl residues (one residue per subunit) are involved in the binding of the substrate to the enzyme. The modified enzyme reversibly regained its activity upon incubation with hydroxylamine. The reactivity of lysyl residues which have been shown to be involved in the active site is markedly reduced in the enzyme inactivated with 1,2-cyclohexanedione, indicating that the lysyl and arginyl residues are in close proximity in the active site.
 ...
PMID:Essential arginyl residues in yeast phosphoglyceromutase. 20 Jun 7

Kinetic parameters of photoinduced permeability increase of artificial lipid membranes, modified by ROS fragments (tau20 degrees C = 20 mesec Ea = 33 +/- 2 kcal/mole) coincides with appropriate parameters of photoinduced protein fluorescence intensity decrease and ROS fragments absorption spectra change (metarhodopsin I leads leads to metarhodopsin II transition). Hydroxylamine accelerates this process, its rate is proportional to hydroxylamine at concentrations lower than 0.6 M.
 ...
PMID:[Molecular mechanisms of receptor. II. Identification of the conformational transition of rhodopsin responsible for the leading edge of the photoresponse of artificial lipid membranes modified by fragments of the outer segment of rods]. 61 19

The kinetics of photoinduced changes of protein fluorescence of cattle visual pigment was studied in the presence of hydroxylamine. The rate constant of fluorescence increase is proportional to NH2OH concentration when it is less than 0.4 M. It reaches the maximal magnitude (3.3 +/- 1 sec-1) at higher hydroxylamine concentration. Fluorescence increase rate is controlled by the rate of chemical reaction of rhodopsin with hydroxylamine. It is limited by conformational rearrangement of opsin. This rearrangement does not induce absorbance spectrum change of visual pigment, but confers to it the capability to react with NH2OH and NaBH4. Kinetic parameters of this rearrangement (tau 20 degrees C approximately 300 msec, Eact = 19 +/- 2 kcal/mole) coincide with kinetic parameters of diminishing of the photoresponse of artificial lipid membrane modified by fragments of rod outer segments in the temperature range studied (+2 divided by +25 degrees C).
 ...
PMID:[Molecular mechanisms of receptor-potential generation by the photoreceptor. III. Conformational transition responsible for the tail end of the photoresponse of an artificial lipid membrane modified by fragments of the external segments of rods]. 61 34

The interaction of diethylpyrocarbonate (DEP) with the pyruvate dehydrogenase component (PDH) isolated from the pyruvate dehydrogenase complex (EC 1.2.4.1) results in a modification of 3-5 histidine residues per mole of enzyme, which simultaneously decreases the enzyme activity. After PDH inhibilion by DEP in the presence of dithiothreitol almost complete reactivation (94%) under the effect of neutral hydroxylamine is observed. In the absence of SH-groups protection incomplete reactivation by hydroxylamine (79%) is found. In the latter case titration with 5,5-dithio--bis-(2-nitrobenzoic acid) in 8 M urea showed that the DEP-modified protein contains less quantity of SH groups (by 4-8) as compared to the native enzyme. It is assumed that the DEP-modified SH-groups are not responsible for the enzyme activity. The differential spectrum of the modified and native PDH showed no changes within the range of 260-300 nm. TPP in combination with Mg2+ (10(-3) M) protectes PDH from being inactivated by DEP. TPP (10(-2) M) reactivates PDH by 70% after its complete inhibition by DEP. Similar protective action is manifested by ATP, ADP and inorganic pyrophosphate in the presence of Mg2+. A kinetic study showed a competitive type of PDH inhibition by DEP with respect to TPP. it is concluded that the histidine residues of PDH are involved in TPP binding.
 ...
PMID:[Role of muscle pyruvate dehydrogenase histidine residues in thiamine pyrophosphate binding]. 98 22

The reaction of O-beta-diethylaminoethylhydroxylamine (O-beta-HA) with cytidine was studied and its mechanism was shown to be analogous to that of the reaction of hydroxylamine of O-methylhydroxylamine with cytidine. In experiments involving reaction of denatured DNA with O-beta-HA., Sephadex G-15 columns were used for the quantitative separation of normal and modified nucleosides after enzymatic hydrolysis of modified DNA by exonuclease A5 followed by alkaline phosphatase treatment. DNA cytidine residues of free cytidine with O-beta-HA. Modified cytidines can form complex with phosphotungstic acid (PTA). It was shown that one mole of PTA was bound per one mole of modified cytidine either in DNA or in free state. Electron microscopic examination of denatured DNA molecules modified by O-beta-HA and reacted with PTA revealed linear arrays of electron-scattering spots which presumably correspond to PTA molecules complexed with modified cytidine in DNA chains.
 ...
PMID:[Double modification of cytidine residues in DNA]. 105 81

0-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride was used to prepare oximes of steroids with keto groups in selected positions; 3,17 and 20-monoketo; 3,17 and 3,20-diketo. Some of the 3-keto steroids had hindered 17-hydroxyl groups which were not readily amenable to esterification with perfluoroanhydrides, the most commonly used derivatizing agents for electron capture gas chromatographic analysis of hydroxy steroids. The oximes were readily prepared from 5 ng of each of the compounds tested, and with testosterone it was demonstrated that the derivative could be prepared from as little as 0.1 ng. The derivatives were stable to gas chromatography and extremely sensitive to electron capture detection. The sensitivity ranged from 1.5 X 10(4) coulombs per mole of progesterone. Because of the ease of preparation of the derivatives, their stability in common solvents and analytical manipulative techniques, the reagent would be suitable for the micro analysis of biologically significant keto steroids by electron capture gas chromatography.
 ...
PMID:0-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride as a sensitive derivatizing agent for the electron capture gas liquid chromatographic analysis of keto steroids. 115 Aug 49

The benzoylarginine peptidase of Treponema denticola (strain ASLM; a human oral spirochaete) was progressively and irreversibly inactivated by 1-(ethoxycarbonyl)-2-ethoxy-1, 2-dihydroquinoline, a carboxyl-group reagent. At acidic pH values, reaction of one mole of the modifier per active site of the enzyme resulted in total inactivation of the enzyme. Assuming that this modifier is a specific carboxyl reagent, the data suggest that the inactivation of the T. denticola benzoylarginine peptidase was caused by the modification of one carboxyl group located close to the active site of the enzyme. Results obtained with Woodward's reagent K (N-ethyl-5-phenylisoxazolium 3'-sulphonate) supported these findings. Carbethoxylation with diethylpyrocarbonate effectively inactivated the enzyme, and addition of hydroxylamine at pH 7.0 restored the activity almost totally, suggesting that the pyrocarbonate had reacted with tyrosyl or histidyl residues.
 ...
PMID:The benzoylarginine peptidase from Treponema denticola (strain ASLM), a human oral spirochaete: evidence for active-site carboxyl groups. 228 Jun 91

Human hepatic microsomal enzymes catalyzed the NADPH-dependent anaerobic reductive activation of [1-14C]metronidazole [1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole] and [4,5-14C]ronidazole [(1-methyl-5-nitroimidazole-2-yl)methyl carbamate] to species that became covalently bound to proteins. Due to the low efficiency of the enzyme-catalyzed covalent binding of metronidazole, the stoichiometry of anaerobic reductive activation was studied with dithionite as the reductant. Two moles of dithionite was consumed per mole of [1-14C]metronidazole for maximal covalent binding to either DNA or immobilized sulfhydryl groups, demonstrating that four electrons are required for the reductive activation of metronidazole. These data implicate the involvement of a hydroxylamine in covalent binding. Maximal covalent binding of [4,5-14C]ronidazole to DNA also required four-electron reduction, consistent with previous studies of the covalent binding of this agent to immobilized sulfhydryl groups [Kedderis et al. (1988) Arch. Biochem. Biophys. 262, 40-48]. Studies of the covalent binding of variously radiolabeled ronidazole molecules to DNA suggested that the imidazole ring was intact while greater than 80% of the 2-carbamoyl group and the C4 proton were not present in the DNA adduct. Studies of both the chemical and human hepatic microsomal reduction of [4-3H]metronidazole demonstrated that covalent binding occurred with the stoichiometric loss of this label, implicating binding at the C4 position. These results suggest that the reductive activation of 5-nitroimidazoles generally proceeds via four-electron reduction to form hydroxylamines followed by nucleophilic attack at C4.
 ...
PMID:Covalent interaction of 5-nitroimidazoles with DNA and protein in vitro: mechanism of reductive activation. 251 18


1 2 3 4 5 Next >>