Synthesis of pyrophosphate coupled to the reverse energy‐linked transhydrogenase reaction in Rhodospirillum rubrum chromatophores

[摘要]

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 (ΔgmH⁺) to drive the phosphorylation of inorganic orthophosphate (P_i) to pyrophosphate (PP_i). The rate of pp_i synthesis is 50 nmol PP_i formed/min per μmol Bchl which is 5% of the rate of light-induced PP_i synthesis. PP_i 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 ΔgmH⁺ generated by the reverse transhydrogenase reaction drives PP_i synthesis. The rate of PP_i synthesis can be partially inhibited by the addition of NADP⁺ a substrate of the forward energy-consuming reaction. The ΔgmH⁺ generated can also be used to drive ATP synthesis by the H⁺-ATPase, but at a lower rate than the pp_i synthesis.

[学科分类] 生物化学/生物物理

[关键词] (Rhodospirillum rubrum) Energy-linked transhydrogenase Pyrophosphate synthesis ATP synthesis Bioluminescence;APS;adenosine 5 '-phosphosulphate;Bchl;bacteriochlorophyll;BSA;bovine serum albumin;DAPP;diadenosine pentaphosphate (Ap5A);DCCD;N;N'-dicyclohexylcarbodiimide;DTE;1;4-dithioerythritol;FCCP;carbonyl cyanide p-trifluoromethoxyhydrazone;PCB−;phenyl dicarbaundecarborane;ANS;8-anilinonaphthalene-1-sulphonic acid;H−-PPase;H−pyrophosphatase;H+ATPase;H+-ATP Synthase