NH2-Terminal Formylmethionine- and NH2-Terminal Methionine-Cleaving Enzymes in Rabbits

Abstract

Staining for peptidase activities on starch gel after the electrophoresis of lysates of rabbit red blood cells or reticulocytes and the identification of the reaction products revealed the existence of the following three enzymes: (a) An enzyme that hydrolyzes NH2-terminal methionine from methionyl peptides longer than tetrapeptides and from shorter methionyl peptides with blocked carboxy ends. This enzyme does not hydrolyze several peptides tested without methionine at the NH2 termini. (b) An enzyme that cleaves formylmethionine from formylmethionyl peptides. This enzyme can also react with acetylmethionyl peptides but does not hydrolyze several peptides tested without an acylmethionine at the NH2 termini. (c) An enzyme that deformylates formylmethionine. This enzyme can hydrolyze various formyl- and acetylamino acids and may be identical with the nonspecific dipeptidase in red cells. These three enzymes exist also in other tissues and are not bound to ribosomes. NH2-terminal methionine and formylmethionine in the short nascent peptides obtained from reticulocytes were hydrolyzed by hemolysates. These findings suggest that biological function of the methionine aminopeptidase and the formylmethionine-releasing enzyme is to remove the terminal methionine and formylmethionine from nascent peptides.