Acyl and amino intermediates in reactions catalysed by pig pepsin. Analysis of transpeptidation products
- 1 March 1976
- journal article
- research article
- Published by Portland Press Ltd. in Biochemical Journal
- Vol. 153 (3) , 691-699
- https://doi.org/10.1042/bj1530691
Abstract
The action of pig pepsin on a variety of small peptides including Leu-Trp-Met-Arg, Leu-Trp-Met, Leu-Leu-NH2, benzyloxycarbonyl-Phe-Leu and Gly-Leu-Tyr was studied. Leu-Leu-Leu was found to be the major product from the substrates Leu-Trp-Met-Arg and Leu-Trp-Met, indicating that the predominant reaction at pH 3.4 was a transpeptidation of the acyl-transfer type. Leu-Leu-Leu was also formed in high yield by amino transfer from benzyloxycarbonyl-Phe-Leu. Like the amino-transfer reactions the acyl transfer proceeded via a covalent intermediate, since [14C]leucine was not incorporated into transpeptidation products and did not exchange with enzyme-bound leucine in the presence of acceptors. With Leu-Trp-Met both acyl and amino transpeptidation products, namely Leu-Leu, Leu-Leu-Leu, Met-Met and Met-Met-Met, were formed in addition to methionine and leucine. With Leu-Trp-Met-Arg (1 mM) the pH optimum for the rates of hydrolysis and acyl transfer is about pH 3.4. At this pH the rate of acyl transfer exceeds that of hydrolysis; at pH 2 hydrolysis was faster than transfer. A comparison of the effect of the length of substrates and products on the reaction rates allows the conclusion that the binding site can extend over 8-9 amino acid residues. Although the experiments provide no conclusive evidence for or against the involvement of amino and/or acyl intermediates in the hydrolysis of long peptides and proteins, the high yield of transpeptidation reactions of both types observed with some substrates suggests a major role for the intermediates in pepsin-catalyzed reactions. When pig pepsin is used for the digestion of proteins for sequence work, the likelihood of the formation of transpeptidation products is considerable. In this way peptides not present in the original sequence could easily form in a reasonably good yield.This publication has 21 references indexed in Scilit:
- Acyl intermediates in penicillopepsin-catalysed reactions and a discussion of the mechanism of action of pepsins.Biochemical Journal, 1975
- Activation of the action of penicillopepsin on leucyl-tyrosyl-amide by a non-substrate peptide and evidence for a conformational change associated with a secondary binding siteBiochemical and Biophysical Research Communications, 1974
- Studies on the Extended Active Sites of Acid ProteinasesProceedings of the National Academy of Sciences, 1974
- Acyl intermediates in pepsin and penicillopepsin catalyzed reactionsBiochemical and Biophysical Research Communications, 1974
- Amino-enzyme intermediates in pepsin-catalyzed reactionsBiochemistry, 1972
- The inhibition of pepsin-catalysed reactions by structural and stereochemical product analoguesBiochemical Journal, 1971
- Mapping the active site of papain with the aid of peptide substrates and inhibitorsPhilosophical Transactions of the Royal Society of London. B, Biological Sciences, 1970
- THE MECHANISM OF PEPSIN ACTIONProceedings of the National Academy of Sciences, 1961
- Pepsin-catalysed transpeptidation of the amino-transfer typeBiochemical Journal, 1959
- [Amino acid determination on paper chromatograms].1957