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 meas urements of laser flash induced absorption changes at 820 nm and 355 n m, 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 ex hibits a kinetic H/D isotope exchange effect of similar magnitude as t hat 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 formatio n comprises the cleavage of at least one hydrogen bond.