CHARACTERIZATION OF 1-AMINOCYCLOPROPANE-1-CARBOXYLATE OXIDASE PARTIALLY PURIFIED FROM CHERIMOYA FRUIT

The enzyme 1-aminocyclopropane-1-carboxylate (ACC) oxidase was extract ed in a soluble form from mesocarp of ripe cherimoya fruit. ACC oxidas e purification to near homogeneity was carried out in three chromatogr aphic steps: anion exchange, chromatofocusing, and gelfiltration. The molecular mass of the purified enzyme was estimated to be 66 kDa by ge l filtration, 62 kDa by native PAGE, and 35 kDa by SDS-PAGE, indicatin g that the enzyme could be active as a dimer. An isoelectric point at pH 4.35 was estimated by chromatofocusing. The activity of semipurifie d enzyme eluted from Mono Q columns required Fe2+, sodium bicarbonate, and ascorbate (K-m = 6.5 mM). The pH optimum was at 7.4 and the appar ent K-m with respect to ACC was 82 mu M in the absence of added sodium bicarbonate (194 mu M in the presence bicarbonate). The particular ch aracteristics of the purified enzyme in relation to the primitive phyl ogenetic position of cherimoya are discussed.