Effects of hydrogen/deuterium exchange on photosynthetic water cleavage in PS II core complexes from spinach

Abstract
H/D isotope exchange effects on P680reduction by Yzand electron abstraction from the water oxidizing complex (WOC) in redox state S3by YZOXwere analyzed in PS II core complexes from spinach by measurements of laser flash induced absorption changes at 820 nm and 355 nm. The results obtained reveal: (1) the rate of YZoxidation by P680is almost independent of the substitution of exchangeable protons by deuterons; and (2) the reaction between YZOXand the WOC in S3exhibits a kinetic H/D isotope exchange effect of similar magnitude as that recently observed in PS II membrane fragments [Renger, G., Bittner, T. and Messinger, J. (1994) Biochem. Soc. Trans. 22, 318–322]. Based on these results it is inferred that photosynthetic dioxygen formation comprises the cleavage of at least one hydrogen bond.

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