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Biomedical subjects

M H Klapper

Publications and source records attributed to M H Klapper.

At least 37 records · Page 2Linked to original sources
PubMed1983

One-electron reduction of flavoproteins: pulse radiolysis of chicken egg white riboflavin binding protein.

Reduction of the chicken egg white riboflavin binding protein by the hydrated electron results in competitive formation of both a disulfide-electron adduct and an anionic flavin semiquinone bound to the protein. The former decays to products that cannot be observed under the conditions of our experiments. The latter is rapidly protonated to the stable neutral semiquinone. The pH dependence of the rate constant associated with this protonation suggests that an acid/base group on the protein donates a proton to the anionic semiquinone.

Animals↗
PubMed1981

alpha-Chymotrypsin deacylation: temperature dependence of hydrolysis and transesterification reactions.

The hydrolysis and transesterification reactions of furoyl-chymotrypsins display nonlinear Arrhenius plots with no apparent discontinuities. Of a number of models considered, the best explanation assumes a temperature-dependent rapid equilibrium between two forms of acyl-enzyme with differing reactivities. Rate constants for the transesterification of alpha-chymotrypsinyl 2-(5-n-propyl)furoate, after normalization for this equilibrium, display a linear free energy correlation with the Taft polarity constants sigma* and volumes of the attacking alcohols.

Acylation↗
PubMed1980

The 'knotting' problem in proteins. Loop penetration.

The 'knotting' problem in proteins is redefined in terms of the more general concept of loop penetration. Disulfide-containing proteins are represented as linear graphs, and it is proposed that proteins with nonplanar graph representations display loop penetrations in their three-dimensional structure. With this argument, it is shown that the occurrence of loop penetration in disulfide-containing proteins is approximately that expected based on the random pairing of sulfhydryl groups. It is argued that loop penetration is not as rare as currently held.

Disulfides↗
PubMed1979

One-electron reduction of flavodoxin. A fast kinetic study.

The reaction kinetics of fully oxidized flavodoxin from Clostridium MP with the hydrated electron have been investigated by the pulse radiolysis method. Four spectrally distinct processes have been observed with the ultimate formation of the singly reduced flavin form of the protein. The last two species obtained in the reaction sequence are spectrally similar, and are connected through a reaction which is first order. It is proposed that this reaction involves a protein conformational alteration.

Clostridium↗
PubMed1979

Trazodone, a new antidepressant: efficacy and safety in endogenous depression.

The effectiveness of trazodone was assessed over a 4-week period under double-blind conditions. Twenty-eight inpatients with a diagnosis of endogenous depression received either trazodone, imipramine, or placebo. Trazodone was significantly better than placebo and frequently better than imipramine according to analyses of the results of the Hamilton Psychiatric Scale for Depression, severity of illness and clinical global improvement ratings, and the Global Ward Behavior Scale. Significant improvement was evident in the trazodone group by the end of the first week of therapy, particularly in those symptoms associated with depression and accompanying anxiety. There were fewer side effects with trazodone than with imipramine.

Adult↗
PubMed1978

Pseudo-dynamic contact surface areas: estimation of apolar bonding.

A new Monte Carlo based algorithm has been written for the computation of pseudo-dynamic contact surface areas. The linear correlation of this contact area with solute transfer free energies (water leads to organic liquid) is established for apolar amino acid side chains. The slope of these linear plots, deltaGosp, is a unitary free energy which has potential use in the estimation of apolar bond free energies in proteins. The magnitude of deltaGosp is dependent upon the nature of the organic solvent involved in the transfer process, varying from 86 to 130 cal/A2. Analogues linear correlations with the same range of deltaGosp values are observed for inhibitors of protein-catalyzed reactions.

Alanine↗
PubMed1978

Kinetics of carbon monoxide binding to singly reduced human methemoglobin.

The kinetics of reaction of singly reduced methemoglobin (HbFe3(3+)Fe2+) with carbon monoxide have been investigated by the pulse radiolysis method. The rate constant for carbon monoxide binding to this form of hemoglobin is 4.1 X 10(6) M-1 S-1 at 24 degrees in our solutions. This value compares with existing values for various forms of hemoglobin ranging from 4 X 10(6) to 6.5 X 10(6) M-1 S-1. Addition of inositol hexaphosphate to the solutions results in a lower rate constant for carbon monoxide binding amounting to 1.1 X 10(5) M-1 S-1.

Carbon Monoxide↗
PubMed1978

Application of pulse radiolysis to the study of proteins: chymotrypsin and trypsin.

The one-electron reduction of chymotrypsin, trypsin, and their zymogens have been studied by pulse radiolysis. The optical spectra of the transient products from the two active enzymes display a pH-dependent band at 360 nm, associated with the histidine-electron adduct. The yield of the histidyl radical as a function of pH is consistent with a pK(a) less than 4.5, which suggests that the radical is located at the enzyme active site. The histidines of the proenzymes chymotrypsinogen and trypsinogen are unreactive towards the hydrated electron. We conclude that formation of the histidine-electron adduct at the serine protease active site is sensitive to the physical alterations which accompany protease activation.

Chymotrypsin↗
PubMed1977

Catalytic activity of Ntau-carboxymethylhistidine-12 ribonuclease: pH dependence.

The pH-dependence of RNAase A and of Ntau-carboxymethylhistidine-12-RNAase (ribonucleate 3'-pyrimidino-oligonucleotidohydrolase) catalysis was studied. Apparent acid dissociation constants were obtained by least squares analysis of the kinetics data. These dissociation constants were compared with pKa values of model imidazole compounds, and with pKa values of histidine residues 12 and 119 on the protein. The shapes of the kcat versus pH profiles for RNAase A and its carboxymethyl derivative are very similar, from which it is concluded that the mechanism of catalysis is closely similar in the two proteins. Apparent pKa values obtained from the kinetic data are higher for the carboxymethylated protein than for RNAase A, as are the pKa values of residues 12 and 119. The similar shifts are consistent with the conclusions that both these residues are functionally significant in native and modified enzyme, and that an unblocked tau-nitrogen on histidine-12 is not essential for activity. From the enzyme's catalytic dependence on pH, and the NMR determined pKa values we propose that histidine 12 and 119 function catalytically in their basic and acidic forms respectively.

Binding Sites↗
PubMed1976

Pulse radiolytic investigation of single heme group reduction in hum an methemoglobin.

Reduction of one of the four heme groups of human aquomethemoglobin A has been investigated by the pulse radiolysis method. The reactivity of e-a-q, the hydrated electron, with methemoglobin was determined by observing this species directly. The separate reactions of the hydroxy yl radical and hydrogen atom, as well as of e-a-q, were studied by observing absorbance changes in the protein spectrum over the wavelength range 290 to 600nm, with appropriate scavengers in solution...

Azides↗
PubMed1976

Rate enhancement specificity with alpha-chymotrypsin: temperature dependence of deacylation.

The relative rate of the hydrolysis of 2-(5-n-alkyl)furoyl-alpha-chymotrypsin reaches a maximum with the propyl derivative. The Arrhenius plots for the hydrolyses of the 2-furoyl-, 2-(5-ethyl)furoyl-, and 2-(5-n-propyl)furoyl-alpha-chymotrypsins display a discontinuity, while the plots obtained with the ramaining furoyl derivatives 5-methyl, 5-n-butyl, and 5-n-amyl are linear. We conclude that the deacylation of the furoyl derivatives of alpha-chymotrypsin involves a minimum of two elementary reaction steps. Depending upon the reaction conditions, rate enhancement specificity appears to be either entropy or enthalpy controlled.

Binding Sites↗
PubMed1975

Catalytic acitivity of Ntau-carboxymethylhistidine-12 ribonuclease.

Ntau-Carboxymethylhistidine-12 RNase is active with both RNA and uridine cyclic 2':3'-monophosphate as substrates. Experimental evidence is presented to show that the activity cannot be due to contaminating RNase A, or other RNase-type protein, to the presence of a mixed dimer between 12- and 119-substituted RNases, or to the presence of trace amounts of Ntau-carboxymethylhistidine-12 RNase. The carboxymethyl derivative has approximately 1 and 13 per cent the specific activity of native enzyme against cyclic 2',3'-UMP at pH 5.0 and 8.5, respectively.

Carboxylic Acids↗