Energy transduction in photosynthetic bacteria. VII. Inhibition of the coupling ATPase by N-ethylmaleimide related to the energized state of the membrane.
N-Ethylmaleimide, at millimolar concentrations, irreversibily inhibits photophosphorylation and ATPase activity of photosynthetic membranes from Rhodopseudomonas capsulata. The inhibitory effect of N-ethylmaleimide is evident only the membranes are preincubated with the inhibitor in the light and in the absence of phosphorylation substrates. ADP and orthophosphate (or arsenate) exert a protective effect against the inhibition if they are present during the preillumination stage. The energization of the membrane by ATP hydrolysis, measured as ATP-induced quenching of 9-aminoacridine fluorescence, also is inhibited irreversibly by N-ethylmaleimide. Uncouplers protect the ATPase from inhibition by N-ethylmaleimide at concentrations at which they inhibit photophosphorylation. The ATPase, as measured either in the dark or in the light, is also inhibited by carbonylcyanide p-trifluoromethoxypenylhydrazone in parallel with photophosphorylation. These results are interpreted as evidence that the high-energy state of the membrane induces a conformational change of the ATPase, making it sensitive to attack by N-ethylmaleimide; this conformational change might be related to the active state of the ATPase.
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D004735:Energy Transfer; D005033:Ethylmaleimide / Q000494:pharmacology*; D006835:Hydrazones / Q000494:pharmacology; D008027:Light; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D010710:Phosphates / Q000494:pharmacology; D010785:Photophosphorylation / Q000187:drug effects*; D012241:Rhodopseudomonas / Q000187:drug effects / Q000378:metabolism*
D006835:Hydrazones; D009570:Nitriles; D010710:Phosphates; D000244:Adenosine Diphosphate; D000251:Adenosine Triphosphatases; D005033:Ethylmaleimide