Bestatin

Bestatin is a specific inhibitor of aminopeptidase B and leucine aminopeptidase. It did not show any inhibition of aminopeptidase A, trypsin, chymotrypsin, elastase, papain, pepsin or thermolysin. Bestatin at 100 pg/ml showed no antibacterial and no antifungal activities. It has low toxicity with no death after intraperitoneal injection of 300 mg/kg to mice.

Bestatin isolated from the culture filtrate of Streptomyces olivoreticuli MD976-C7. The structure of bestatin was elucidated to be (2S, 3R)-3-amino-2-hydroxy-4- phenylbutanoyll-(S)-leucine. Bestatin itself was not hydrolyzed by either of the enzymes, when bestatin was incubated as substrate, L-leucine was not detected by thin-layer chromatography.

Unlike the case of orthophenanthroline, the inhibitory activity of bestatin on aminopeptidase B was not reversed by addition of zinc ion. Bestatin has a pair of adjacent amino and hydroxyl groups, which shows metal-complexing activity. If the inhibitory activity of bestatin is attributable to five-membered chelate ring formation by a pair of adjacent amino and hydroxyl groups of bestatin and a metal ion of the enzyme, the isomers having erythro AHPA, which is difficult to form a chelate ring, are expected not to show inhibitory activity. However, the isomers having erythro-AHPA or (2S, 3S)-AHPA showed marked inhibitory activity. Bestatin and its active isomers are effective due to a mechanism other than a chelating action at the active center.