The catalytic activity of pig pepsin C towards small synthetic substrates

• Published in: Biochemical journal Vol. 179; no. 1; pp. 239 - 246
• Main Authors: Auffret, C A, Ryle, A P
• Format: Journal Article
• Language: English
• Published: England 01.04.1979
• Subjects: Animals; Catalysis; Hydrogen-Ion Concentration; Hydrolysis; Kinetics; Pepsin A - antagonists & inhibitors; Pepsin A - metabolism; Peptides - chemical synthesis; Peptides - metabolism; Substrate Specificity; Swine; Tyrosine
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj1790239

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.