Characteristics of six isoperoxidases from Korean radish root

Two cationic isoperoxidases (designated C1 and C3) and four anionic isoperoxidases (designated A1, A2, A3n and A3) 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 C1, C3, A1 and A2 were ca 44,000, while anionic isoperoxidase A3n and A3 have M(r)s of 31,000 and 50,000, respectively. Deglycosylated A2 and C3 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 A1, A2, A3n and A3) and one cationic isoperoxidase C3 were determined. N-Terminal amino acid sequences were determined for A1, A3n and C3, while A2 was found to have a blocked amino terminal residue. Kinetic studies with respect to various synthetic and naturally occurring substrates were also investigated.