Slow, tight binding and competitive aminopeptidase (AP) inhibitor. Inhibits cytosolic leucine aminopeptidase, microsomal aminopeptidase M and bacterial leucine aminopeptidase, human serum aminopeptidase A (AP-A), aminopeptidase N (AP-N), tyrosine aminopeptidase, but not aminopeptidase B (AP-B). Amastatin is without effect on trypsin, papain, chymotrypsin, elastase, pepsin or thermolysin. Inhibits completely the Suc-Ala-Ala-Pro-Leu-pNA amidolytic enzyme. Slightly inhibits the formation of angiotensin III (Ang III) from Angiotensin II through AP-A, but significantly increases the potency of angiotensin III and-angiotensin I. Moderate inhibitor of mitochondrial intermediate peptidase (MIP). Weak inhibitor of simian immunodeficiency virus protease (SIV-PR).