Multiple Forms of Aminopeptidases in Representatives of the Tribe Vicieae (Leguminosae)

Abstract

The distribution of aminopeptidases with activity against aminoacyl β-naphthylamide substrates has been studied in several close relatives of pea (Pisum sativum L.), a species known to possess two forms of aminopeptidase distinguished by their insensitivity (AP1) or complete sensitivity (AP2) to the chelator 1,10-phenanthroline. Leaf, cotyledon or embryo extracts exhibited one or two bands of aminoacyl β-naphthylamidase activity following electrophoresis, yet test-tube assays for enzyme activity conducted with the same extracts in the absence or presence of 5 mM phenanthroline suggested a distribution of isoenzymes similar to that of pea in every instance. Better resolution of isoenzymes was obtained by anion exchange chromatography with diethylaminoethyl-Sephadex A-50, using the fraction of protein precipitating between 35% and 55% of saturation with ammonium sulfate as a concentrated source of isoenzymes. When the phenanthroline-insensitive activity was inactivated by dialysis at pH 4.7, then two phenanthroline sensitive forms, AP2 and AP3, could be distinguished from cotyledons of sweet pea (Lathyrus odoratus L.) and broad bean (Vicia faba L.). Embryos of lentil (Lens culinaris Medik.) yielded single forms corresponding to AP1 and AP2 of pea; however, the AP1 from lentil showed partial sensitivity to phenanthroline, the degree of inhibition depending on the substrate employed.