REVERSED ENERGY CONVERSION REACTIONS OF BACTERIAL PHOTOPHOSPHORYLATION

The final steps of the reactions leading to the formation of inorganic pyrophosphate (PPi) or ATP in bacterial photophosphorylation have been shown by us to be reversible to the level of electron transport in chromatophores from Rhodospirillum rubrum by addition of either of these two compounds in the dark. This reversal of photophosphorylation reactions, which is more rapid and larger with PPi than with ATP, results in a change in the redox state of at least two endogenous components of the electron transport chain, i.e. a reduction of b-type cytochrome and an oxidation of cytochrome c2. The half-time for the PPi-induced changes was around 0.4 sec which was one-tenth of the half-time when ATP was used as the energy donor. Some of the characteristics of the PPi-induced b-type cytochrome changes are described, such as the relationship between concentration of PPi and steady state redox level of b-type cytochrome, as well as the dependence of the reduction of this compound on concentration of Mg++-ion. Mn++, Zn++, and Co++ may substitute for Mg++ as co-factors. Ca++ inhibits the PPi-induced changes. The sensitivity to the inhibitors antimycin A, gramicidin D, p-trifluoromethoxy-carbonylcyanide-phenylhydrazone (FCCP), 2,6-dinitro-4-isooctylphenol (octyl-DNP), desaspidin and oligomycin has also been studied. © 1969.