Biomedical subjects

A P Ryle

Publications and source records attributed to A P Ryle.

3 recordsLinked to original sources

PubMed1979

The catalytic activity of pig pepsin C towards small synthetic substrates.

A series of small peptides has been synthesized and used to investigate the activity of a minor pig pepsin, pepsin C (EC 3.4.23.3). The peptides had the general formula A-Leu-Val-His-B. B was either OMe, NH2 or OH. With B = NH2 hydrolysis (kcat./Km) at 37 degrees C and pH 2.07 increased as A was Ac-Ala, Ac-Tyr, Ac-Phe and Ac-Ala-Phe. The pH dependence of the hydrolysis of Ac-Phe-Leu-Val-His-NH2 indicated the apparent pKa values of two catalytically important groups on the enzyme as 1.42 and 4.88. Inhibition of the hydrolysis of the same peptide by Ac-Phe at pH 3.01 showed a form of mixed non-competitive inhibition. Hydrolysis of Ac-Tyr-Leu-Val-His-OMe and the corresponding amide showed non-classical kinetics, which are discussed in terms of a substrate-activating mechanism. The results are discussed with reference to observations made by other workers on pig pepsin A.

Animals↗

PubMed1979

The specificity of some pig and human pepsins towards synthetic peptide substrates.

1. The peptidase activities of pig pepsins A and C and human pepsin and gastricsin were compared. 2. The peptides studied had the general formula A Leu Val-His-B. Hydrolysis at 37 degrees C and pH 2.07 occurred at the amino side of the leucine residue for all the enzymes and all the peptides. 3. When A was Ac-Ala the peptides were hydrolysed under these conditions slowly by pig pepsin C only. 4. Pig pepsin A and human pepsin were unable to hydrolyse the tyrosine-containing peptides under the conditions tested. Gastricsin (human pepsin C) had about one-third of the activity of pig pepsin C with these substrates. 5. The increase in the rate of hydrolysis caused by the extension of the chain by a single alanine residue was most marked for pig pepsin A and human pepsin.

Animals↗

PubMed1975

Purification, properties and amino acid sequence of atypical cytochrome c from two protozoa, Euglena gracilis and Crithidia oncopelti.

A basic cytochrome was isolated from the phytomastigophorean protozoan Euglena gracilis and a similar protein from the zoomastigophorean protozoan Crithidia oncopelti. In both cases chromatography on CM-cellulose in first the reduced and then the oxidized form proved to be an efficient means of purification. The two cytochromes can be classed in the cytochrome c family but they have certain atypical features. The alpha peak of the absorption spectrum is shifted towards the red and is asymmetrical. The pyridine ferrohaemochrome has an alpha-peak maximum intermediate between that of c-type cytochromes and proteins containing protohaem IX. The test for free vinyl groups was positive. The amino acid sequences of the two cytochromes were determined. Attention is drawn in the text to those parts of the evidence that are less satisfactory. Both sequences are homologous with the family of cytochrome c, but are unusual in having only one cysteine residue so that the haem is attached through only one thioether bond. Detailed evidence for the amino acid dequences of the two proteins has been deposited as Supplementary Publication SUP 50042 (70 pages) at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Wetherby, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1975) 145, 5.

Amino Acid Sequence↗