How is Kreb's cycle regulated by ADP?

[sameeralord]

My textbook says,

Increase in the concentration of ADP accelerates the rate of reactions that use ADP to generate ATP. If ADP is present in limiting concentration, the formation of ATP by oxidative phosphorylation decreases owing to lack of phosphate acceptor or inorganic phosphate. As NADH and FADH2 accumulate, their oxidized forms become depleted, causing the oxidation of acetyl CoA by TCA cycle to be inhibited, owing to lack of oxidized coenzymes.

I checked the whole citric acid cycle, and only the conversion of succinyl coA requires ADP or GDP. I don't understand how a lack of this would make NADH accumulate. Could anyone explain this. Thanks a lot

 

[DanP]

My textbook says,I checked the whole citric acid cycle, and only the conversion of succinyl coA requires ADP or GDP. I don't understand how a lack of this would make NADH accumulate. Could anyone explain this. Thanks a lot

All dehydrogenases involved in Krebs are sensitive to the redox potential (mainly NADH / NAD+ ratio). NADH is an inhibitor of those enzymes. Since Electron transport chain & oxidative phosphorylation produce ATP relaying on NADH to provide the energy for ADP phosphorylation to ATP, you can then say ATP is an inhibitor. So the cycle is "turned on" by high ADP/ATP or NAD+ / NADH ratios.

IIRC, the rate limiting enzime in Krebs is isocitric dehydrogenase.