A Novel Type of Substrate Specificity of Rice BAPAase (Benzoyl-L-atginine p-nitroanilide Hydrolase) with Mixed Endopeptidase and Carboxypeptidase

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The substrate specificity of rice embryo benzotyl-L-arginine p-nitroanilide hydrolyze (BAPAase) was examined. No endopeptidase activity toward protein substrates was detectable. Small peptides (less than 8 residues) and amide, ester substrates, however, were hydrolyzed very well at the carboxyl side of the lysine or arginine residue. No other peptide bond was hydrolyzed. The N-terminal arginine of the substrates was released very slowly. Peptides with lysine or arginine penultimate to the C-terminal position were hydrolyzed well and released an amino acid. The oxidized insulin B chain (30 residues) was cleaved very slowly at the C-terminal Lys-Ala bond, whereas an Arg-Gly bond at an inner position was not cleaved. The hydrolytic rate increased after the chain length was shortened by chymotryptic digestion. These results show that the rice embryo BAPAase is a novel enzyme which has mixed endopeptidase-carboxypeptidase activity toward the Arg-X and Lys-X bonds of small peptides, a characteristic intermediate between trypsin and serine carboxypeptidase. This enzyme may act in the break-down of small peptides that have physiological functions.
日本植物生理学会の論文