Morpeth F F, Massey V
Biochemistry. 1982 Mar 16;21(6):1307-12. doi: 10.1021/bi00535a031.
Initial rate measurements were made of the oxidation of D-lactate and D-alpha-hydroxybutyrate by oxygen and potassium ferricyanide, catalyzed by D-lactate dehydrogenase from Megasphera elsdenii. The detailed kinetic work indicates a "ternary complex" type mechanism, with a complex of keto acid and reduced enzyme reacting with the electron acceptor at pH 8. However, as the pH is lowered, the double-reciprocal plots become nonlinear, with a downward curvature. This seems to be due to negative interactions within the protein rather than to a complexity of the kinetic mechanism. The variation of initial rate parameters at pH 8 with temperature yields nonlinear Arrhenius plots with a greater activation energy above the break point than below. This type of behavior has been previously reported only for fumarase (Massey, 1953). Studies with deuterated D-lactate show only a small isotope effect on phi 0 and phi 1 (KM/Vmax for lactate) but a large effect on phi 2 (Km/Vmax for ferricyanide).
对埃氏巨型球菌的D - 乳酸脱氢酶催化氧气和铁氰化钾氧化D - 乳酸和D - α - 羟基丁酸的初始速率进行了测定。详细的动力学研究表明，在pH 8时，存在一种“三元复合物”类型的机制，即酮酸和还原型酶的复合物与电子受体发生反应。然而，随着pH值降低，双倒数图变得非线性，呈现向下弯曲。这似乎是由于蛋白质内部的负相互作用，而非动力学机制的复杂性所致。在pH 8时，初始速率参数随温度的变化产生非线性的阿伦尼乌斯图，断点以上的活化能大于断点以下的活化能。这种行为类型此前仅在延胡索酸酶中报道过（梅西，1953年）。对氘代D - 乳酸的研究表明，其对φ0和φ1（乳酸的KM/Vmax）只有很小的同位素效应，但对φ2（铁氰化钾的Km/Vmax）有很大影响。
