Johnson R E, Rupley J A
Biochemistry. 1979 Aug 7;18(16):3611-6. doi: 10.1021/bi00583a027.
The association reactions of NADH and NAD+ with dimeric pig heart supernatant malate dehydrogenase (s-MDH) have been measured at pH 6 and 8 by calorimetric and fluorescence methods, and the thermodynamic parameters describing these reactions have been evaluated. Coenzyme binding is associated with the uptake of 0.55 mol of H+/mol of NADH at pH 8 and 0.19 mol of H+ at pH 6. No significant effect of NAD+ binding on proton binding was observed. Increase in ionic strength strongly affects the free energies of binding of NAD+ and NADH. No cooperativity was observed in the enthalpy or free energy changes for binding of NAD+ or NADH. The differences in free energy of binding of NAD+ and NADH and the effect of pH on binding of NADH are entropy based. These effects are interpreted as reflecting a small number of interactions within the active site that are predominantly ionic.
已通过量热法和荧光法在pH 6和8条件下测定了NADH和NAD⁺与二聚体猪心上清液苹果酸脱氢酶（s-MDH）的缔合反应，并评估了描述这些反应的热力学参数。辅酶结合在pH 8时伴随着每摩尔NADH摄取0.55摩尔H⁺，在pH 6时摄取0.19摩尔H⁺。未观察到NAD⁺结合对质子结合有显著影响。离子强度的增加强烈影响NAD⁺和NADH的结合自由能。在NAD⁺或NADH结合的焓变或自由能变化中未观察到协同性。NAD⁺和NADH结合自由能的差异以及pH对NADH结合的影响是基于熵的。这些效应被解释为反映了活性位点内少量主要为离子性的相互作用。
