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

HID isotope exchange effects on P680(+.) reduction by Y-z and electron abstraction from the water oxidizing complex (WOC) in redox state S-3 by Y-Z(OX) were 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 Y-z oxidation by P680(+.) is almost independent of the substitution of exchangeable protons by deuterons; and (2) the reaction between YOZOX and the WOC in S-3 exhibits 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.