Characteristics of six isoperoxidases from Korean radish root

Abstract

Two cationic isoperoxidases (designated C 1 and C 3) and four anionic isoperoxidases (designated A 1, A 2, A 3n and A 3) from Korean radish ( Raphanus sativus L.) root have been purified to apparent homogeneity, and some of their enzymatic properties were characterized. All six isoperoxidases are glycoproteins composed of a single polypeptide chain. The M r s Of C 1, C 3, A 1 and A 2 were ca 44 000, while anionic isoperoxidase A 3n and A 3 have M r s of 31 000 and 50 000, respectively. Deglycosylated A 2 and C 3 by trifluoromethanesulphonic acid treatment showed M r s of 37 000 and 40 000, respectively, suggesting that the carbohydrate contents for these isoenzymes are 14 and 9%, respectively. Relative amino acid compositions of four anionic isoperoxidases (designated A 1, A 2, A 3n and A 3) and one cationic isoperoxidase C 3 were determined. N-Terminal amino acid sequences were determined for A 1, A 3n and C 3, while A 2 was found to have a blocked amino terminal residue. Kinetic studies with respect to various synthetic and naturally occurring substrates were also investigated.