Proton uptake by the chloroplast cytochrome bf complex
1989
Hope, A.B. | Rich, P.R.
The proton uptake, delta Hn+, associated with turnover of the quinone reduction site (here termed the Qn site -- see abbreviations) of the chloroplast cytochrome bf complex has been kinetically resolved. It was approximately correlated with cytochrome f rereduction in a range of conditions. delta Hn+ was inhibited by the quinol oxidation site (here termed the Qp site -- see abbreviations) inhibitors stigmatellin and DBMIB, but was unaffected by NQNO, an effector of the quinone reduction site (the Qn site), or by antimycin A. At external pH of 6 and 8, delta Hn+ was equivalent to about one proton per Photosystem I per flash, i.e., each turnover of the complex caused a proton uptake. At intermediate pH values on the first flash this value was lower, but it rose to around 1 on subsequent flashes, provided that they were given sufficiently rapidly. Comparable measurements were made in the absence of nonactin so that a transmembrane potential difference was present during proton uptake. This potential, of the order of 30-50 mV, had little effect on the extent of delta Hn+.
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