Specificity of proteolysis inhibitors in rabbit plasma.

Hydrolysis and inhibition of hydrolysis of leucine enkephalin in Oryctolagus plasma were studied by kinetics and chromatographic techniques. By data obtained, in this species, enkephalins are degraded by the same enzymes active in other mammals: aminopeptidases, dipeptidylaminopeptidases, and dipeptidylcarboxypeptidases. At variance with data obtained in other species, where enkephalins are hydrolyzed mostly by aminopeptidases, in Oryctolagus Leu-enkephalin hydrolysis is mainly due to dipeptidylcarboxypeptidases, whereas aminopeptidases contribution is the minimum of all three enzyme groups. Comparative analyses performed in the presence and in the absence of plasma inhibitors indicate that the ability of these substances to reduce substratum hydrolysis is very limited. On the contrary, the specific hydrolysis pattern evidenced appears to originate primarily from selective inhibition of the three groups of enzymes. Results obtained appear consistent with a role of plasma inhibitors in tuning hydrolysis to specific substrata, without appreciably modifying the amount of the substratum degraded.