[Components of cyclic electron transport in stromal subchloroplast particles enriched with photosystem I]

The effects of specific electron transport inhibitors (e. g. Hg2+, dibromothymoquinone, antimycin A) on photo-induced oxidation-reduction of P700, electrochromic pigment changes and ATP yields in the photophosphorylation reactions of PS I-enriched subchloroplast particles, were studied. The results obtained suggest that in the absence of exogenous cofactors the cyclic electron transport proceeds through plastoquinone and plastocyanine molecules, partly maintained in the preparations. The low ATP production is correlated with the low rates of an electron transfer. The cyclic transfer increases to some extent after addition of exogenous plastocyanine; in addition to the above-mentioned carriers it includes also cytochrome b6; however, the electron flow in this case is not coupled with phosphorylation. None of these components are involved in cyclic electron transport in the presence of reduced DCIP, which ensures the ATP synthesis via an artificial loop for proton translocation.