title: The catalytic activity of pig pepsin C towards small synthetic substrates.
abstract: 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.
mesh_terms: D000818:Animals; D002384:Catalysis; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D010434:Pepsin A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010455:Peptides / Q000138:chemical synthesis / Q000378:metabolism*; D013379:Substrate Specificity; D013552:Swine; D014443:Tyrosine
chemical_list: D010455:Peptides; D014443:Tyrosine; D010434:Pepsin A