On the Specificity of Human Gastricsin and Pepsin

Digests of oxidized ribonuclease A and glucagon with human gastricsin and pepsin have been compared with IR-120 B column chromatography and two-dimensional high voltage paper electrophoresis to separate the resulting peptides.The amino-terminal residues and the amino acid compositions of purified peptides were determined in order to establish the sequence of peptides and hence the sites of cleavage by the two enzymes.Evidence is presented indicating that the specificities of both enzymes are broad and similar.However, from the studies with protein as well as synthetic dipeptide substrates, definite ditIerences have been shown.Kinetic parameters, V,, and Km, for the hydrolysis of several benzyloxycarbonyl-L-tyrosyl peptides and benzyloxycarbonyl-L-tryptophanyl peptides with gastricsin were compared.The effect on the hydrolysis rate of side chains in the amino acid residues of the substrates was elucidated.