Isolation and Some Properties of an Aminopeptidase from the Primary Leaf of Wheat (Triticum aestivum L.)

The isolation and characterization of the AP1 form of aminopeptidase (EC 3.4.11.) previously identified (Waters, Dalling 1979 Aust J Plant Physiol 6: 595-606) in the primary leaves of wheat (Triticum aestivum L. cv Egret) seedlings is reported. The enzyme shows a high preference for a substrate which contains an aromatic side chain, whether this be either a synthetic beta-naphthylamide or a peptide substrate. Maximum activity with both types of substrates occurred around pH 7.6. The stability of AP1 was reduced by exposure to high pH and by incubation at temperatures above 20 degrees C in the absence of substrate. AP1 was inhibited by the metal chelators bathocuproine and bathophenanthroline and the sulfhydryl group inhibitors p-chloromercuribenzoate and N-ethylmaleimide. The molecular weight, estimated by gel filtration, was 57,000. The K(m) value for activity against the synthetic substrate Phe-beta-NA (0.20 millimolar) was slightly lower than that for Phe-Phe (0.50 millimolar) although the enzyme activity against peptide substrates was considerably greater than with Phe-beta-NA.