or LDH, this is important in destroying a waste product of anaerobic metabolism during exercise. Lactate buildup is countered by this enzyme breaking it down into pyruvate, which can be used normally. Of course, this requires NAD to be available - something that is in short supply in the active muscle. Therefore, lactate is transported in the blood to the liver, where it is broken down. It also works in the other direction in some circumstances, making lactate from pyruvate. Indeed, this is what is occuring during exercise where it reduces NADH for use in oxidative phosphorylation.

It was proposed that LDH co-operates with another dehydrogenase, GAPDH, to cycle the cofactor between them. With one enzyme reducing NAD and the other oxidising NADH, this would allow both reactions to be more efficient. The greatest efficiency would come from a direct, ternary complex between the two tetramers with the NAD(H) channeling between them. This seems a little unlikely, since the resulting metabolon would have to associate and dissociate under different physiological conditions.

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