Abstract
Chemical modification of Rhodospirillum rubrum chromatophores by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) results in inactivation of photophosphorylation, Mg 2+-ATPase, oxidative phosphorylation and ATP-driven transhydrogenase, with apparent first-order kinetics. Other energy-linked reactions such as light-driven transhydrogenase and light-dependent proton uptake were insensitive to NBD-Cl. The Ca 2+-ATPase activity of the soluble coupling factor from chromatophores ( R. rubrum F 1) was inactivated by NBD-Cl with kinetics resembling those described for Mg 2+-ATPase and photophosphorylation activities of chromatophores. Both NBD-chromatophores and NBD- R. rubrum F 1 fully recovered their activities when subjected to thiolysis by dithioerythritol. Phosphoryl transfer reactions of chromatophores and Ca 2+-ATPase activity of R. rubrum F 1 were fully protected by 5 mM P i against modification by NBD-Cl. ADP or ATP afforded partial protection. Analysis of the protection of Ca 2+-ATPase activity by P i indicated that NBD-Cl and P i are mutually exclusive ligands. Spectroscopic studies revealed that tyrosine and sulfhydryl residues in R. rubrum F 1 underwent modification by NBD-Cl. However, the inactivation was only related to the modification of tyrosine groups.
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