Bovine-lens leucine aminopeptidase. Kinetic studies with activators and competitive inhibitors.

Abstract

An attempt has been made, by means of kinetic experiments, to get some insight into the molecular mechanism of the binding and catalytic steps taking place during low‐molecular‐weight substrate hydrolysis by leucine aminopeptidase from bovine eye lenses. To this end the variation of the kinetic parameters with concentration and type of well‐known activators (anions and metal cations of valency two) was studied systematically.Additional, we searched for substrate‐like competitive inhibitors. It was found that the end product l‐leucine shows no competition but the compounds N‐p‐tosyl‐N′‐butylcarbamide and N‐sulfanilyl‐N′‐butylcarbamide turned out to be rather potent competitive inhibitors with Ki values comparable to the Km of l‐leucine‐p‐nitroanilide. The variation of the ki values with temperature was studied so that the thermodynamic parameters of inhibitor binding could be calculated.In order to be able to make a meaningful comparison between the kinetic parameters all data were subjected to a computer‐aided (CDC 1604‐A) statistical analysis.