Creighton D J, Rose I A
J Biol Chem. 1976 Jan 10;251(1):69-72.
The enzyme from cod fish muscle that catalyzes the irreversible decarboxylation of oxalacetate and is homogeneous by several criteria contains very significant pyruvate kinase activity. For every unit of decarboxylase activity (0.90 unit/mg) there are 235 units of pyruvate kinase activity (212 units/mg). The inability to separate the two activities by a variety of physical techniques indicates that both are due to a single enzyme protein. Improtantly, the two activities appear to take place at the same or overlapping sites on the enzyme. Phosphoenolpyruvate and 4-ethyloxalacetate are strong linear competitive inhibitors of the decarboxylase activity with respect to oxalacetate having dissociation constants of 3.2 and 10.2 muM, respectively, while 4-ethyloxalacetate is a linear competitive inhibitor of the pyruvate kinase activity with respect to phosphoenolpyruvate, Ki - 13.5 muM. In addition, both activities exhibit sigmoidal kinetics for substrates. The differential influence of effectors on substrate cooperativity for the two reactions indicates that the decarboxylase reaction may be an important tool for studying allosteric mechanisms in this enzyme.
来自鳕鱼肌肉的一种酶能催化草酰乙酸的不可逆脱羧反应，且通过多种标准判断该酶是均一的，它具有非常显著的丙酮酸激酶活性。每单位脱羧酶活性（0.90单位/毫克）对应235单位的丙酮酸激酶活性（212单位/毫克）。无法通过多种物理技术将这两种活性分离，这表明它们都归因于单一的酶蛋白。重要的是，这两种活性似乎在酶上的相同或重叠位点发生。磷酸烯醇丙酮酸和4 - 乙基草酰乙酸是草酰乙酸脱羧酶活性的强线性竞争性抑制剂，相对于草酰乙酸，它们的解离常数分别为3.2和10.2微摩尔，而4 - 乙基草酰乙酸是丙酮酸激酶活性相对于磷酸烯醇丙酮酸的线性竞争性抑制剂，Ki为13.5微摩尔。此外，两种活性对底物均表现出S形动力学。效应物对这两个反应底物协同性的不同影响表明，脱羧酶反应可能是研究该酶变构机制的重要工具。
