Ting I P
Department of Life Sciences, University of California, Riverside, California 92502.
Plant Physiol. 1968 Dec;43(12):1919-24. doi: 10.1104/pp.43.12.1919.
Phosphoenolpyruvate carboxylase was purified from corn root tips about 80-fold by centrifugation, ammonium sulfate fractionation, and anion exchange and gel filtration chromatography. The resulting preparation was essentially free from malate dehydrogenase, isocitrate dehydrogenase, malate enzyme, NADH oxidase, and pyruvate kinase activity. Kinetic analysis indicated that l-malate was a noncompetitive inhibitor of P-enolpyruvate carboxylase with respect to P-enolpyruvate (K(I) = 0.8 mm). d-Malate, aspartate, and glutamate inhibited to a lesser extent; succinate, fumarate, and pyruvate did not inhibit. Oxaloacetate was also a noncompetitive inhibitor of P-enolpyruvate carboxylase with an apparent K(I) of 0.4 mm. A comparison of oxaloacetate and l-malate inhibition suggested that the mechanisms of inhibition were different. These data indicated that l-malate may regulate CO(2) fixation in corn root tips by a feedback or end product type of inhibition.
通过离心、硫酸铵分级分离、阴离子交换和凝胶过滤色谱法，从玉米根尖中纯化出磷酸烯醇式丙酮酸羧化酶，纯化倍数约为80倍。所得制剂基本不含苹果酸脱氢酶、异柠檬酸脱氢酶、苹果酸酶、NADH氧化酶和丙酮酸激酶活性。动力学分析表明，L-苹果酸是磷酸烯醇式丙酮酸羧化酶对磷酸烯醇式丙酮酸的非竞争性抑制剂（K(I)=0.8 mM）。D-苹果酸、天冬氨酸和谷氨酸的抑制作用较小；琥珀酸、延胡索酸和丙酮酸无抑制作用。草酰乙酸也是磷酸烯醇式丙酮酸羧化酶的非竞争性抑制剂，表观K(I)为0.4 mM。草酰乙酸和L-苹果酸抑制作用的比较表明，抑制机制不同。这些数据表明，L-苹果酸可能通过反馈或终产物类型的抑制作用来调节玉米根尖中的CO₂固定。
