ISOLATION AND PROPERTIES OF A CARBOXYPEPTIDASE FROM COTYLEDONS OF GERMINATED MUNG BEAN-SEEDS

A serine-type carboxypeptidase (EC 3.4.16.1) present in cotyledons of mung bean (Vigna radiata) seedlings was purified up to the step where only a doublet of polypeptides with molecular mass of 43 and 45 kDa, r espectively, was detected by SDS-PAGE. The enzyme is thought to be a s ingle chain monomer, as the molecular mass of the enzyme determined by gel filtration is 55 kDa. Although the isolation of each peptide in n ative form was not successful, the SDS-treated peptides could be separ ately isolated by preparative electrophoresis. These two polypeptides are immunologically homologous. When proangiotensin is used as a subst rate, the enzyme releases amino acid residues in the order of the C-te rminal sequence of this oligopeptide chain. This enzyme belongs to the class of serine-type carboxypeptidases, judging from the effects of v arious protease inhibitors on the enzyme activity. The enzyme preferen tially catalyzes the hydrolysis of the peptide bonds formed by the car boxyl group of hydrophobic amino acids. Western immunoblot profiles re veal that the enzyme is absent in cotyledons during the early stages a fter imbibition and that it begins to increase only after 2-3 days.