Species-dependence of the redox potential of the primary quinone electron acceptor QA in photosystem II verified by spectroelectrochemistry.

The redox potentials E(m)(Q(A)/Q(A)(-)) of the primary quinone electron acceptor Q(A) in oxygen-evolving photosystem II complexes of three species were determined by spectroelectrochemistry. The E(m)(Q(A)/Q(A)(-)) values were experimentally found to be -162+/-3 mV for a higher plant spinach, -171+/-3 mV for a green alga Chlamydomonas reinhardtii and -104+/-4 mV vs. SHE for a red alga Cyanidioschyzon merolae. On the basis of possible deviations for the experimental values, as estimated to differ by 9-29 mV from each true value, plausible causes for such remarkable species-dependence of E(m)(Q(A)/Q(A)(-)) are discussed, mainly by invoking the effects of extrinsic subunits on the delicate structural environment around Q(A). Copyright 2010 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.