KINETIC STUDIES OF GLUTAMATE DEHYDROGENASE WITH GLUTAMATE AND NORVALINE AS SUBSTRATES - COENZYME ACTIVATION AND NEGATIVE HOMOTROPIC INTERACTIONS IN ALLOSTERIC ENZYMES
KINETIC STUDIES OF GLUTAMATE DEHYDROGENASE WITH GLUTAMATE AND NORVALINE AS SUBSTRATES - COENZYME ACTIVATION AND NEGATIVE HOMOTROPIC INTERACTIONS IN ALLOSTERIC ENZYMES
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DOI：
10.1042/bj1150621
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发表时间：
1969-01-01
影响因子：
4.1
通讯作者：
DALZIEL, K
中科院分区：
文献类型：
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作者：
ENGEL, PC;DALZIEL, K
1.谷氨酸脱氢酶的动力学研究进行了广泛的浓度范围内的辅酶NAD+和NADP+和底物谷氨酸和正缬氨酸。评价初始速率参数。2.从Michaelis-Menten行为向更高的活动的偏差，观察到与浓度增加的任一辅酶与谷氨酸作为底物，但不是与正缬氨酸作为底物。3.在pH 7·0的磷酸盐缓冲液中，以任一辅酶为变量和恒定的大谷氨酸浓度的Lineweaver-Burk图显示出三个或四个斜率不同的线性区域，具有相对尖锐的不连续性。外推法得到的最大速率和米氏常数随辅酶浓度的增加而逐步增加。4.在没有证据的酶和辅酶制剂的异质性，结果被解释在酶亚基之间的负同向相互作用。有人建议，在Lineweaver-Burk图或相互结合图的尖锐的不连续性可能是这种新型的相互作用，这可以解释的Adair-Koshland模型，但不是由莫诺，怀曼和Changeux模型的特点。
1. Kinetic studies of glutamate dehydrogenase were made with wide concentration ranges of the coenzymes NAD+and NADP+and the substrates glutamate and norvaline. Initial-rate parameters were evaluated. 2. Deviations from Michaelis–Menten behaviour towards higher activity were observed with increasing concentrations of either coenzyme with glutamate as substrate, but not with norvaline as substrate. 3. In phosphate buffer, pH7·0, Lineweaver–Burk plots with either coenzyme as variable and a constant, large glutamate concentration showed three or four linear regions of different slope with relatively sharp discontinuities. Maximum rates obtained by extrapolation and Michaelis constants for the coenzymes increased in steps with increase of coenzyme concentration. 4. In the absence of evidence of heterogeneity of the enzyme and coenzyme preparations, the results are interpreted in terms of negative homotropic interactions between the enzyme subunits. It is suggested that sharp discontinuities in Lineweaver–Burk plots or reciprocal binding plots may be characteristic of this new type of interaction, which can be explained in terms of an Adair–Koshland model, but not by the model of Monod, Wyman & Changeux.