Myers D E, Tolbert B, Utter M F
Biochemistry. 1983 Oct 25;22(22):5090-6. doi: 10.1021/bi00291a007.
Chicken liver pyruvate carboxylase has an absolute requirement for short-chain acyl coenzyme A (CoA), whereas the same enzyme from yeast has less stringent requirements. The yeast enzyme has now been studied in an effort to elucidate the mechanism by which acyl-CoA stimulates pyruvate carboxylase activity. Yeast pyruvate carboxylase has an apparent basal level of activity above which CoA and acyl-CoAs of 2-20 carbons activate; the concentration of acyl-CoA required for half-maximum activation (K0.5) decreases as the chain length of the acyl moiety increases to 16 carbons. Activation of yeast pyruvate carboxylase by acyl-CoA is brought about in part by increasing the affinity of pyruvate carboxylase for two substrates, bicarbonate and pyruvate. The affinity of pyruvate carboxylase for bicarbonate is also increased by potassium ions. The observation of only low levels of activity in the absence of acyl-CoA or potassium ion leads to the conclusion that the basal activity so frequently referred to is probably due to the presence of activating monovalent cations. Pyruvate carboxylase from yeast probably has an absolute requirement for monovalent cations or acyl-CoA with a combination of the two being required for optimum conditions for maximal activity. Stimulation by acyl-CoA and inhibition by aspartate are mutually antagonistic with each affecting the activation or inhibition constant and the degree of cooperativity brought about by the other. The enzyme from liver is unaffected by aspartate.
鸡肝丙酮酸羧化酶对短链酰基辅酶A（CoA）有绝对需求，而酵母中的同一种酶的需求则没那么严格。目前对酵母中的这种酶进行了研究，以阐明酰基辅酶A刺激丙酮酸羧化酶活性的机制。酵母丙酮酸羧化酶有一个明显的基础活性水平，在此之上，CoA和含2至20个碳的酰基辅酶A会产生激活作用；激活达到半数最大活性所需的酰基辅酶A浓度（K0.5）会随着酰基部分链长增加至16个碳而降低。酰基辅酶A对酵母丙酮酸羧化酶的激活作用部分是通过提高丙酮酸羧化酶对两种底物（碳酸氢盐和丙酮酸）的亲和力来实现的。钾离子也会提高丙酮酸羧化酶对碳酸氢盐的亲和力。在没有酰基辅酶A或钾离子的情况下仅观察到低水平活性，这导致得出这样的结论：经常提到的基础活性可能是由于存在激活的单价阳离子。酵母中的丙酮酸羧化酶可能对单价阳离子或酰基辅酶A有绝对需求，两者结合是达到最大活性最佳条件所必需的。酰基辅酶A的刺激作用和天冬氨酸的抑制作用相互拮抗，各自影响对方的激活或抑制常数以及协同程度。肝脏中的这种酶不受天冬氨酸影响。
