Millay R H, Schilling H, Hersh L B
J Biol Chem. 1978 Mar 10;253(5):1371-7.
Phosphoenolpyruvate carboxylase from Pseudomonas MA grown on methylamine as a sole carbon source is an allosteric enzyme activated by NADH. Activation is accompanied by a change in the sedimentation value of the enzyme from 12 S to 9 S. In this paper ADP is shown to be an inhibitor of the enzyme. ADP has its most potent effect on the NADH-activated enzyme. Kinetics of ADP inhibition in the presence of NADH and of NADH activation in the presence of ADP are allosteric. The presence of ADP prevents the decrease in sedimentation value in the presence of NADH. Cross-linking studies indicate that the 12 S form of the enzyme is a tetramer of identically sized subunits and that the 9 S form corresponds to a dimer. The cross-linked enzyme is active and is activated by NADH and inhibited by ADP. It is proposed that NADH and ADP are a regulatory pair for this enzyme and reflect the energy status of the organism, allowing the carboxylase to control the flow of carbon into anabolic or catabolic pathways.
以甲胺作为唯一碳源生长的假单胞菌MA中的磷酸烯醇丙酮酸羧化酶是一种由NADH激活的别构酶。激活伴随着酶的沉降值从12 S变为9 S。本文表明ADP是该酶的抑制剂。ADP对NADH激活的酶具有最强的作用。在存在NADH的情况下ADP抑制的动力学以及在存在ADP的情况下NADH激活的动力学都是别构的。ADP的存在可防止在存在NADH的情况下沉降值降低。交联研究表明，该酶的12 S形式是大小相同的亚基的四聚体，而9 S形式对应于二聚体。交联后的酶具有活性，可被NADH激活并被ADP抑制。有人提出，NADH和ADP是该酶的一对调节因子，反映了生物体的能量状态，使羧化酶能够控制碳进入合成代谢或分解代谢途径的流量。
