Chromatophores from the photosynthetic bacterium Rhodospirillum rubrum contain a membrane-bound transhydrogenase catalyzing the transfer of a hydride ion between NADH and NADP+. The reverse reaction, i.e. reduction of NAD+ by NADPH, can furnish sufficient energy (Δ \ ̃gmH+) to drive the phosphorylation of inorganic orthophosphate (Pi) to pyrophosphate (PPi). The rate of ppi synthesis is 50 nmol PPi formed/min per μmol Bchl which is 5% of the rate of light-induced PPi synthesis. PPi synthesis is inhibited by both the H+-PPase inhibitor fluoride and the specific transhydrogenase inhibitor palmitoyl-CoA. The effects of both DCCD and uncouplers on the system provide additional evidence that the Δ \ ̃gmH+ generated by the reverse transhydrogenase reaction drives PPi synthesis. The rate of PPi synthesis can be partially inhibited by the addition of NADP+ a substrate of the forward energy-consuming reaction. The Δ \ ̃gmH+ generated can also be used to drive ATP synthesis by the H+-ATPase, but at a lower rate than the ppi synthesis. © 1986.
Nore, B. F., Husain, I., Nyrén, P., & Baltscheffsky, M. (1986). Synthesis of pyrophosphate coupled to the reverse energy-linked transhydrogenase reaction in Rhodospirillum rubrum chromatophores. FEBS Letters, 200(1), 133–138. https://doi.org/10.1016/0014-5793(86)80525-7