Photoinactivation of photophosphorylation and dark ATPase in Rhodospirillum rubrum chromatophores |
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Authors: | Luit Slooten Christiaan Sybesma |
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Institution: | Vrije Universiteit Brussel, Department of Biophysics, Pleinlaan 2, B-1050, Brussels, Belgium |
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Abstract: | Preillumination of Rhodospirillum rubrum chromatophores with strong, far-red light in the presence of phenazine methosulfate under non-phosphorylation conditions results in a selective, irreversible inactivation (typically about 70%) of photophosphorylation and of uncoupler-stimulated dark ATPase. The time course of the photoinactivation is similar to the light-on kinetics of the light-induced proton uptake in the absence of ADP. Only little photoinactivation occurs when the uncoupler carbonyl cyanide m-chlorophenyl hydrazone is present or when phenazine methosulfate is absent during the preillumination, indicating that the reaction occurs only when the membrane is energized. Phosphorylation conditions offer a practically complete protection against the photoinactivation. Inorganic phosphate, Mg2+ or ADP do not provide a significant protection against the photoinactivation, nor does ATP. The pH-dependence of the reaction(s) leading to photoinactivation may indicate that a partial reaction of the photophosphorylation process (perhaps only a conformational change of the coupling factor) precedes the photoinactivation. |
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Keywords: | PMS phenazine methosulfate CCCP |
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