O2、ACC和CO2对番木瓜ACC氧化酶活性的影响

研究了番木瓜果皮l-氨基环丙烷-l-羧酸(ACC)氧化酶的部分纯化,底物(O2和ACC)浓度、辅助因子(CO2和Fe2+)和抑制剂(Co2+和α-氨基异丁酸)对体外乙烯产生速率的影响.通过DEAE-Sepharose和Phenyl-Sepharose柱层析后,番木瓜果皮ACC氧化酶被纯化了19.5倍.在乙烯产生中,ACC氧化酶对O2的Km值主要取决于ACC的浓度,随着ACC水平的增加而下降;当O2的浓度增加时,酶对ACC的Km值降低.CO2显著地增加酶的活性以及对O2和ACC的Km值.Fe2+提高酶的活性,Co2+抑制酶的活性;Fe2+能够拮抗Co2+对酶活性的抑制作用.这些动力学资料表明ACC氧化酶遵循一种顺序结合机制,首先与02结合,然后与ACC结合.

Effect of O2 , ACC and CO2 Concentration on the Activity of Partially Purified ACC Oxidase from Papaya

1 -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 (CO2 and Fe2+) and inhibitors(Co2+ 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 Km value by ACC oxidase for O2 in ethylene production varied greatly depending on the ACC concentration, and decreased with increase of ACC levels. The Km value for ACC also declined as oxygen concentration increased. The enzyme activity was dramatically increased by CO2,and the Km value for O2 and for ACC increased with increase of CO2 concentration. Enzyme activities were obviously increased by Fe2+ and significantly inhibited by Co2+; and Fe2+ could antagonize the inhibitory role of Co2+ 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 O2 and then to ACC.