ISOLATION AND CHARACTERIZATION OF A MUNG BEAN LEAF POLYPHENOL OXIDASE

Crude extracts from mung bean leaves, roots, stems and dark grown seed lings contained multiple forms of polyphenol oxidase (PPO) with subuni t M-r values of 65 x 10(3), 59 x 10(3), 52 x 10(3), 47 x 10(3), 31 x 1 0(3) and 21 x 10(3). Only two of these forms were present in broken an d intact leaf chloroplasts. A mature form of PPO, purified to apparent homogeneity from leaf chloroplasts, contained two proteins with subun it M-r,values of 65 x 10(3) and 59 x 10(3), respectively. The purified enzyme had a pH optimum of 6.0, a pi of 5.1, and oxidized a variety o f a-diphenols. The K-m for L-dopa was 24 mM. o-Diphenol oxidation was inhibited by salicyl hydroxamic acid and 2,3-naphthalenediol, whereas metkimazole, tropolone and 4-hexylresorcinol only resulted in partial inhibition. (C) 1997 Elsevier Science Ltd.