Fisher H F, Subramanian S, Stickel D C, Colen A H
J Biol Chem. 1980 Mar 25;255(6):2509-13.
The reaction catalyzed by bovine L-glutamate dehydrogenase is subjected to allosteric activation by ADP. We have measured the thermodynamic parameters (delta G0, delta H0, delta S0, and delta Cp) of the formation of the various possible binary and ternary complexes formed between the enzyme, NADPH, and either ADP or its analogs, adenosine, AMP, and ATP. delta H0 and delta Cp have been measured by flow calorimetry; delta G0 values obtained by calorimetry itself, differences spectroscopy, or gel filtration have been selected on the basis of accuracy under the conditions required for the formation of each complex. The data are interpreted in terms of "interaction parameters," the differences between the thermodynamic parameters of the formation of a ternary complex and the sum of those of the two related binary complexes. Both adnosine and ATP appear to loosen the binding of NADPH by simply preventing a subsite interaction of NADPH. AMP appears to have only minor and probably secondary effects. The negative effect of the binding of ADP on that of NADPH, however, involves the formation of a new interaction, which is exothermic, entropy compensated, has a moderately large negative delta Cp, and does not occur in either binary complex.
牛L-谷氨酸脱氢酶催化的反应受到ADP的变构激活作用。我们已经测量了在酶、NADPH与ADP或其类似物腺苷、AMP和ATP之间形成的各种可能的二元和三元复合物的热力学参数（ΔG0、ΔH0、ΔS0和ΔCp）。通过流动量热法测量了ΔH0和ΔCp；根据每种复合物形成所需条件下的准确性，选择了通过量热法本身、差示光谱法或凝胶过滤获得的ΔG0值。这些数据根据“相互作用参数”进行解释，即三元复合物形成的热力学参数与两个相关二元复合物的热力学参数之和之间的差异。腺苷和ATP似乎只是通过阻止NADPH的亚位点相互作用来减弱NADPH的结合。AMP似乎只有轻微且可能是次要的影响。然而，ADP的结合对NADPH结合的负面影响涉及形成一种新的相互作用，这种相互作用是放热的、熵补偿的，具有适度大的负ΔCp，并且在任何一个二元复合物中都不会发生。
