Delayed light studies on photosynthetic energy conversion. VIII. Evidence from millisecond emission of chloroplasts for two adenylate binding sites on membrane-bound coupling factor, CF 1

Abstract

Effects of adenylates on chloroplast delayed light emission, at millisecond dark times, are inverse to the previously characterized effects of adenylates on electron transport rates. Either ADP alone or ATP alone increase intensity of delayed light, while ADP plus P i decrease it. ADP alone requires the presence of an electron acceptor to have this effect on delayed light, but ATP does not. All three adenylate effects are abolished by uncoupling with gramicidin, by partial removal of photophosphorylation coupling factor (CF 1) with EDTA, and by antibody to CF 1. Readdition of CF 1 re-established the adenylate effects in EDTA-stripped membranes. The three adenylate effects are differentially sensitive to pH, and pH differentially affected their abolition by antibody to CF 1. The two adenylate effects shown in the absence of P i are exhibited at lower adenylate concentrations than the ADP plus P i effect, and are also less sensitive to phloridzin. These results are discussed in terms of probable adenylate effects on membrane-bound chloroplast coupling factor, CF 1. At least two ADP binding sites would differ with respect to adenylate concentration for half maximal binding; pH of optimal binding capacity; phloridzin sensitivity; and functional regulation of electron transport, proton uptake, and energy storage within the membrane as measured by delayed light emission. It remains unclear whether the high affinity ADP binding site is identical to a high affinity ATP binding site on CF 1.