Inhibition and metal ion activation of pig kidney aminopeptidase P. Dependence on nature of substrate

Article abstract of DOI:10.1016/0006-2952(96)00180-3

Pig kidney aminopeptidase P (AP-P; EC 3.4.11.9) has been purified to homogeneity after its solubilisation from brush border membranes by phosphatidylinositol-specific phospholipase C. The effects of various activators and inhibitors of AP-P activity have been examined with a number of different substrates for the enzyme. The hydrolysis of bradykinin and ArgProPro is inhibited at Mn²⁺ concentrations above 10^-5 M, whereas the hydrolysis of other substrates (GlyProHyp, β-casomorphin, substance P) is substantially activated, with 4-10 mM Mn²⁺ being optimal. The thiol reagent, p-chloromercuriphenylsulphonic acid, inhibits the hydrolysis of GlyProHyp but markedly activates the hydrolysis of bradykinin. A number of inhibitors of angiotensin converting enzyme (ACE; EC 3.4.15.1), previously reported to inhibit the hydrolysis of GlyProHyp, have no effect on the hydrolysis of bradykinin except in the presence of Mn²⁺. Differences were also observed in the degree of inhibition of GlyProHyp and bradykinin hydrolysis by EDTA and their reactivation by divalent cations. The hydrolysis of GlyProHyp follows Michaelis-Menten kinetics with a K(m) value of 2.7 mM. Bradykinin inhibits GlyProHyp hydrolysis with an I₅₀ of 1.4 μM. The hydrolysis of bradykinin by AP-P reveals anomalous nonlinear kinetics indicative of negative cooperativity or the presence of more than one active site for this substrate. These results indicate that substrates for AP-P can be divided into 2 groups based on their responses to inhibitors and cation activators.