Effect of O2, ACC and CO2 concentration on the activity of partially purified ACC oxidase from papaya

Abstract

Aminocyclopropane 1 carboxlic acid (ACC) is oxidized to form ethylene by ACC oxidase. The partial purification of ACC oxidase from fruit peels of papaya and effects of substrates (oxygen and ACC), cofactors (CO 2 and Fe 2+ ) and inhibitors (Co 2+ and α aminoisobutyric acid) on in vitro ethylene production rate were investigated. ACC oxidase has been purified 19.5 fold by using DEAE Sepharose and Phenyl Sepharose columns. The K m value by ACC oxidase for O 2 in ethylene production varied greatly depending on the ACC concentration, and decreased with increase of ACC levels. The K m value for ACC also declined as oxygen concentration increased. The enzyme activity was dramatically increased by CO 2, and the K m value for O 2 and for ACC increased with increase of CO 2 concentration. Enzyme activities were obviously increased by Fe 2+ and significantly inhibited by Co 2+ ; and Fe 2+ could antagonize the inhibitory role of Co 2+ . These kinetic data are consistent with the view that the catalytic role of ACC oxidase follows an ordered binding mechanism in which ACC oxidase binds first to O 2 and then to ACC.