How does ADP affect the activity of isocitrate dehydrogenase according to the chapter?

ADP enhances the activity of isocitrate dehydrogenase by promoting allosteric activation. This results in all subunits of the enzyme adopting an active conformation, which lowers the apparent Km for isocitrate, allowing it to bind more readily and increasing the reaction rate.

In the presence of ADP, isocitrate dehydrogenase exhibits positive cooperativity, where the binding of isocitrate to one subunit facilitates the activation of other subunits. This leads to a significant decrease in the apparent Km for isocitrate, meaning that even small changes in ADP concentration can lead to substantial increases in the enzyme's activity. Consequently, the enzyme operates more efficiently at the isocitrate concentrations typically found in the mitochondrial matrix.