Dehydrogenases cooperative effects

Fig. 20.13. Allosteric regulation of isocitrate dehydrogenase (ICDH). Isocitrate dehydrogenase has eight subunits, and two active sites. Isocitrate, NAD, and NADH bind in the active site ADP and Ca are activators and bind to separate allosteric sites. A. A graph of velocity versus isocitrate concentration shows positive cooperativity (sigmoid curve) in the absence of ADP. The allosteric activator ADP changes the curve into one closer to a rectangular h5 perbola, and decreases the (S0.5) for isocitrate. B. The allosteric activation by ADP is not an all-or-nothing response. The extent of activation by ADP depends on its concentration. C. Increases in the concentration of product, NADH, decrease the velocity of the enzyme through effects on the allosteric activation.

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