NAD+-malic enzyme. Regulatory properties of the enzyme from Ascaris suum.
NAD+-malic enzyme. Regulatory properties of the enzyme from Ascaris suum.
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NAD-苹果酸酶。
DOI：
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发表时间：
1976
影响因子：
4.8
通讯作者：
B. G. Harris
中科院分区：
文献类型：
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作者：
W. Landsperger;B. G. Harris
本文研究了猪蛔虫线粒体中依赖NAD的苹果酸酶的调节特性。苹果酸饱和曲线呈S型，且随pH的升高而增加。富马酸是唯一被测试的化合物，它能刺激酶的活性，而草酸乙酯是最强的抑制物。低水平的富马酸激活与苹果酸具有竞争性。提示这种刺激对控制寄生虫体内的错位反应具有生理意义。支链挥发性脂肪酸排泄产物齐格罗、2-甲基丁酸酯和2-甲基戊酸对酶活性有抑制作用，这种抑制作用与苹果酸竞争。这些化合物的Ki值在其浓度的生理范围内，因此，它们可能有助于控制体内苹果酸酶的活性。草酰乙酸酯对苹果酸酶活性的抑制作用与苹果酸竞争，其Ki值随pH的升高而降低。提出了两种替代方案，这两种方案可以解释蛔虫苹果酸酶缺乏草乙酸酯脱羧基的原因。
The regulatory properties of the NAD-dependent malic enzyme from the mitochondria of Ascaris suum have been studied. The malate saturation curve exhibits sigmoidicity and the degree of this sigmoidicity increases as the pH is increased. Fumarate was the only compound tested that stimulated the enzyme activity, whereas oxalacetate was the most powerful inhibitor. Activation by low levels of fumarate was found to be competitive with malate. It is proposed that this stimulation has physiological significance in controlling the dismutation reaction in the parasite. The branched-chain volatile fatty acid excretion products, tiglate, 2-methylbutanoate, and 2-methylpentanoate, inhibited the enzyme activity and this inhibition was competitive with malate. The Ki values for these compounds are in the physiological range of their concentrations; therefore, it is suggested that they may aid in controlling the malic enzyme activity in vivo. Oxalacetate inhibition of malic enzyme activity was competitive with malate, and the Ki values decreased with an increase in pH. Two alternatives are proposed which could account for the lack of oxalacetate decarboxylation by the ascarid malic enzyme.