Pepstatin A is of microbial origin and is an N-acyl-pentapeptide, more accurately: isovaleryl-L-valyl-L-valyl-statyl-L-alanyl-statine. Pepstatin A was found to be a potent competitive inhibitor of most aspartic proteases but a weak inhibitor of renin.
Microbial product, chymostatin was discovered by H. Umezawaet al.v in 1970 by testing the anti-chymotrypsin activity of culture filtrates. Since the amino acid analysis of different samples gave variable ratios of phenylalanine, leucine, valine and isoleucine, chymostatin was considered to be a mixture of similar peptides with minor differences. Attempts to separate the components were unsuccessful.