ACC oxidase from Carica papaya: Isolation and characterization

Most of the studies done on I-aminocyclopropane I-carboxylic acid (ACC) oxidase were done in vivo. It is only recently that in vitro studies have been carried out successfully on the enzyme. Here we report on in vitro studies of the enzyme that was isolated from Carica papaya. The enzyme had a K-m of 37 mu M and was inhibited by M-propyl gallate (0.240 mM), sodium dithionite (0.022 mM), sodium metabisulphite (0.021 mM) and cobalt sulphate (0.100 mM). The activity of the enzyme increased with ripening, the enzyme was somewhat labile and activity was lost after 4 days at 14 degrees C; activity was prolonged when the crude homogenate was kept at - 15 degrees C. Isolation and purification were achieved with ammonium sulphate precipitation followed by gel-filtration (Sephadex G 100-120) and ion-exchange chromatography (DEAE-Sephadex). Gel electrophoresis of the purified enzyme gave a single band which corresponded to a molecular mass of 27.5 kDa. The amino acid content of the enzyme showed a relatively high percentage of valine (10.4%). Enzyme activity was enhanced when dithiothreitol (3 mM) and bicarbonate ion (30 mM) were added to the assay medium. The production of ethylene from Carica papaya did not require pretreatment of the fruit with ethylene.