Neimark H, Tung M C
J Bacteriol. 1973 Jun;114(3):1025-33. doi: 10.1128/jb.114.3.1025-1033.1973.
Acholeplasma laidlawii A possesses a nicotinamide adenine dinucleotide (NAD)-dependent l(+)-lactate dehydrogenase (LDH) which is activated specifically by low concentrations of fructose-1, 6-diphosphate (FDP). Studies with partially purified enzyme show that the kinetic response to FDP is hyperbolic. The enzyme is inhibited by inorganic phosphate, adenosine triphosphate, and high concentrations of reduced NAD (NADH). Low activity is demonstrable in the absence of FDP at pH 6.0 to 7.2, but FDP is absolutely required in the region of pH 8. FDP causes an upward shift in the optimum pH of the enzyme, which is near 7.2 in tris (hydroxymethyl)aminomethane buffer. Activation of the enzyme by FDP is markedly affected by substrate concentration; FDP lowers the apparent K(m) for pyruvate and NADH. The affinity of the enzyme for pyruvate is also influenced by H(+) concentration. The pyruvate analogue alpha-ketobutyrate serves as an effective substrate for the enzyme; when it is utilized, the enzyme is still activated by FDP. Reversal of the pyruvate reduction reaction catalyzed by the enzyme can be demonstrated with the 3-acetylpyridine analogue of NAD. The catalytic properties of the A. laidlawii enzyme and the known FDP-activated LDHs which occur among lactic acid bacteria are discussed.
莱氏无胆甾原体A含有一种烟酰胺腺嘌呤二核苷酸（NAD）依赖性L（+）-乳酸脱氢酶（LDH），该酶可被低浓度的果糖-1,6-二磷酸（FDP）特异性激活。对部分纯化酶的研究表明，其对FDP的动力学反应呈双曲线型。该酶受到无机磷酸盐、三磷酸腺苷和高浓度还原型NAD（NADH）的抑制。在pH 6.0至7.2且无FDP的情况下，酶活性较低，但在pH 8的区域则绝对需要FDP。FDP会使酶的最适pH值上移，在三（羟甲基）氨基甲烷缓冲液中，最适pH值接近7.2。FDP对酶的激活作用受到底物浓度的显著影响；FDP会降低丙酮酸和NADH的表观K（m）值。酶对丙酮酸的亲和力也受H（+）浓度的影响。丙酮酸类似物α-酮丁酸可作为该酶的有效底物；当使用α-酮丁酸时，该酶仍可被FDP激活。用NAD的3-乙酰吡啶类似物可证明该酶催化的丙酮酸还原反应的可逆性。本文讨论了莱氏无胆甾原体酶与乳酸菌中已知的FDP激活型LDH的催化特性。
