Photo phosphorylation associated with photosystem ii part 2 effects of electron donors catalyst oxidation and electron transport inhibitors on photosystem ii cyclic photo phosphorylation

Yocum, C.F.

Plant Physiology (Rockville) 60(4): 592-596


ISSN/ISBN: 0032-0889
Accession: 006109026

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Incubation of KCN-Hg-NH2OH-inhibited spinach (Spinacia oleracea L.) chloroplasts with p-phenylenediamine for 10 min in the dark prior to illumination produced rates of photosystem II cyclic photophosphorylation up to 2-fold greater than the rates obtained without incubation. Partial oxidation of p-phenylenediamine with ferricyanide produced a similar stimulation of ATP synthesis; addition of dithiothreitol suppressed the stimulation observed with incubation. Addition of ferricyanide in amounts sufficient to oxidize completely p-phenylenediamine failed to inhibit completely photosystem II cyclic activity. This is due at least in part to the fact that the ferrocyanide produced by oxidation of p-phenylenediamine is itself a catalyst of photosystem II cyclic photophosphorylation. N,N,N',N'-Tetramethyl-p-phenylenediamine catalyzes photosystem II cyclic mine. The activities of both proton/electron and electron donor catalysts of the photosystem II cycle are inhibited by dibromothymoquinone and antimycin A. Apparently photosystem II cylcic photophosphorylation requires the operation of endogenous membrane-bound electron carriers for optimal coupling of ATP synthesis to electron transport.