曲酸对小菜蛾酚氧化酶抑制作用的研究

Inhibitory Effects of Kojic Acid on Phenoloxidase of Diamondback Moth Plutella xylostella

研究了曲酸对小菜蛾酚氧化酶的单酚酶和二酚酶活力的影响并初步探讨了其抑制作用机理,结果表明,曲酸对小菜蛾酚氧化酶的单酚酶和二酚酶活力均有抑制作用,其I50分别为0.07 mmolL-1和1 mmolL-1。曲酸对单酚酶活力表达的迟滞时间有明显的延长效应,对二酚酶的抑制作用表现为典型的可逆竞争型抑制类型,其抑制常数Ki为0.47 mmolL-1。曲酸与酚氧化酶中催化氧化反应活性中心的Cu2+鳌合可能是其产生抑制作用的重要原因。金属铁离子可明显地缩短单酚酶的迟滞时间,但对单酚酶的活力无明显影响。

The effects of Kojic acid on phenoloxidase (PO) of Plutella xylostella were studied, when which had been partially purified by 40% saturated [(NH4)2SO4] and Sephadex G-100 gel filtration. Kojic acid showed inhibitory effets on both monophenolase and o-diphenolase activity of the PO. The inhibitor concentrations leading to 50% (I50) activity lost were estimated to be 0.07 mmolL-1 for monophenolase activity and 1 mmolL-1 for diphenolase, respectively. Kojic acid can also prolong the lag time of PO for oxidation of L-tyrosine. The inhibitory kinetics were analyzed by Lineweaver-Burk plots and kojic acid was found to be a reversible competitive inhibitor with the Ki of 0.47 mmolL-1. The ability of kojic acid to inhibit the enzyme activity may be associated with its ability to chelate copper at the active site. In addition, the iron ion was found to shorten the lag time obviously, but have no important effect on the monophenolase activity.