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Y Yuthavong

Publications and source records attributed to Y Yuthavong.

79 records · Page 5Linked to original sources
PubMed1975

Some chemical characteristics of dimethylsuberimidate and its effect on sarcoplasmic reticulum vesicles.

Sarcoplasmic reticulum vesicles treated with dimethylsuberimidate lose the capacity for ATP-promoted Ca2+ accumulation and show other properties indicative of leaky vesicles. As an aid to assessing whether this effect was caused by cross-linking or by hydrolysis products, characteristics of dimethylsuberimidate hydrolysis under incubation conditions used were measured. At pH 7.0, 25 DEGREES C, dimethylsuberimidate is hydrolyzed with an apparent first order rate constant of 0.016 min-1, to give dimethylsuberate as the principal product. The effect on ATP-promoted Ca2+ accululation was shown to be caused by partially and fully hydrolyzed products of the diimido ester, and not to cross-linking of membrane components.

Adenosine Triphosphate↗
PubMed1971

Kinetic specificity in papain-catalysed hydrolyses.

The specificity of the proteolytic enzyme, papain, for the peptide bond of the substrate adjacent to that about to be cleaved and for the acyl residue of some N-acylglycine derivatives is manifest almost exclusively in the formation of the acyl-enzyme from the enzyme-substrate complex. Models for the enzyme-substrate complex and acyl-enzyme intermediate are suggested that account for these observations. In particular it is suggested that the peptide bond of the substrate adjacent to that about to be cleaved, is bound in the cleft of the enzyme between the NH group of glycine-66 and the backbone C=O group of aspartic acid-158, and provides a sensitive amplification mechanism through which the specificity of the enzyme for hydrophobic amino acids such as l-phenylalanine is relayed. It is also suggested that the distortion in the enzyme-substrate complex and the binding of the peptide bond adjacent to that about to be cleaved are also linked and behave co-operatively, the distortion of the protein facilitating binding and the stronger binding facilitating distortion. The results imply that between the enzyme-substrate complex and the acyl-enzyme a relaxation of the protein conformation must occur.

Anilides↗
PubMed1971

pH-dependence and structure-activity relationships in the papain-catalysed hydrolysis of anilides.

The pH-dependence of the Michaelis-Menten parameters for the papain-catalysed hydrolysis of N-acetyl-l-phenylalanylglycine p-nitroanilide was determined. The equilibrium binding constant, K(s), is independent of pH between 3.7 and 9.3, whereas the acylation constant, k(+2), shows bell-shaped pH-dependence with apparent pK(a) values of 4.2 and 8.2. The effect of substituents in the leaving group on the acylation constant of the papain-catalysed hydrolysis of hippuryl anilides and N-acetyl-l-phenylalanylglycine anilides gives rise in both series to a Hammett rho value of -1.04. This indicates that the enzyme provides electrophilic, probably general-acid, catalysis, as well as the nucleophilic or general-base catalysis previously found. A mechanism involving a tetrahedral intermediate whose formation is general-base-catalysed and whose breakdown is general-acid-catalysed seems most likely. The similarity of the Hammett rho values appears to exclude facilitated proton transfer as a means through which the specificity of papain is expressed.

Anilides↗