Succinate-linked NAD+ reduction

Succinate-linked NAD reduction by R. rubrum chromatophores can be driven by PPj [9,10,88] according to the following equations ... 

The opposite effects are observed with the succinate-linked NAD reduction. The NAD reduction is inhibited over 50% by PPj-driven ATP formation, but ATP formation is not inhibited at all by NAD reduction. NAD reduction apparently requires a higher level of than does the transhydrogenase. Thus, competing... 

Mitochondria from adult H. diminuta exhibit an NADH-coupled fumarate reductase (Table 5.11). This presents a potential dilemma with respect to the utilisation of intramitochondrial reducing equivalents by this worm. As reducing equivalents are generated by the malic enzyme in the form of NADP, a mechanism for the transfer of hydride ions from NADPH to NAD to produce NADH is required so that electron-transport-associated activities can proceed and terminate with the reduction of fumarate to succinate. Such a mechanism does exist in H. diminuta as there is a non-energy-linked, membrane-associated transhydrogenase (214, 217, 221, 476). This transhydrogenase, which also occurs in H. microstoma (216) and Spirometra mansonoides (220) catalyses the reaction ... 

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