Distribution and Characteristics of Aminoacyl β-Naphthylamidase Activities in Wheat Seedlings

Abstract

Gel electrophoretic studies have revealed that crude extracts from various tissues of wheat seedlings contain two major enzymes capable of hydrolysing aminoacyl ß-naphthylamides. A third enzyme which exclusively hydrolyses the ß-naphthylamides of the imino acids proline and hydroxyproline has also been demonstrated in wheat leaves. The pH optimum for ß-naphthylamidase activity against phenylalanine ß-naphthylamide in crude extracts was 7.4. The two major enzymes differ with respect to their substrate specificities; the more anionic enzyme, APl, hydrolyses a relatively narrow range of hydrophobic aminoacyl substrates including the ß-naphthyIamides of leucine, phenylalanine, methionine, tyrosine and tryptophan, while the enzyme of lower electrophoretic mobility, AP2, hydrolyses a broad range of substrates. The two enzymes also differ in their sensitivity to the metal chelator 1,10-phenanthroline. The AP2 enzyme from wheat, like that from pea, appears to be a metallo-enzyme, but APl does not show any sensitivity to phenanthroline. The results of developmental studies performed with wheat seedling tissues are consistent with the view that the naphthylamidase enzymes function as aminopeptidases in vivo. A close association was observed between total enzyme activity and soluble protein content, with the highest naphthylamidase activities being found in actively growing tissues.