Synthetic peptide and ester substrates for rennin

Summary Rennin hydrolysed the phe-met bond in the peptide H-ser-leu-phe-met-ala-OMe (i.e. methyl ester), the amino acid sequence of which is similar to that around the phe-met bond attacked by rennin in κ-casein. Rennin did not attack other peptides from this sequence not containing serine, and it is suggested that, in both κ-casein and the pentapeptide, the enzymic attack is accelerated by the nearby serine side chain. Rennin also hydrolysed sulphite esters such as phenyl sulphite ester and some N-substituted imidazole compounds such as benzoyl imidazole. Phenyl sulphite esters may be suitable substrate for assaying the activity of preparations of rennin.