A Peptidase (Aminopeptidase B) from Cat and Guinea Pig Liver Selective for N-Terminal Arginine and Lysine Residues. II. Modifier Characteristics and Kinetic Studies.

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Abstract
Some modifier characteristics and kinetic properties of an aminopeptidase from cat and guinea pig liver were studied and the results compared with those of rat liver aminopeptidase B. The activity of the three enzymes on L-arginine and L-lysine [beta] -naphthylamides was inhibited strongly in the presence of exceedingly small amount of Hg2+, Pb2+, Cd2+, and p-chloromercuribenzoate and to a lesser extent by other heavily metal ions. None of the chelating agents used (8-OH-quinoline, EDTA, 1,10-phenanthroline and KCN) significantly inhibited the function of these enzymes. Diethyl p-nitrophenylphosphate and di-isopropyl fluorophosphate had no effect. Neither cysteine nor 2-mercaptoethanol activated the enzymes. The most significant effect was the activation by certain monovalent anions, notably chloride ions. The Michaelis constant for the hydrolysis of L-arginine-[beta] -naphthylamide was determined for the three enzymes, as well as the energy of activation for the hydrolysis of L-arginine-and L-lysine-[beta] -naphthylamide. All of the results obtained with the cat and guinea pig preparation were very similar to those obtained with the rat liver enzyme. Therefore, there exists an enzyme in guinea pig and cat liver corresponding to that of rat liver, i. e. aminopeptidase B.