Evaluation of a novel aminopeptidase N inhibitor, in vitro, using two assay systems.

The activities of the novel aminopeptidase N inhibitor (APNI), beta-Amino-alpha-Hydroxyl-Phenyl butanic acid-Valine (AHPA-Val), were compared with APNI (amastatin). AHPA-Val and amastatin produced competitive inhibition of the hydrolysis of Tyr-Gly in the guinea-pig striatal membrane preparation, with K(i) equal to 14.06 microM and 12.48 microM respectively. Met-enkephalin-induced twitch inhibition of the guinea-pig ileum preparation was enhanced by AHPA-Val and amastatin with pA(1/2) values (the negative logarithm concentration of APNI that decreased the IC(50) of Met-enkephalin by half), of 7.08 and 7.79 respectively. These results suggest that AHPA-Val has good activity as an APNI and that these two assay systems are useful for evaluating the potency of novel APNIs.