Hydrogen peroxide oxidation catalyzed by chloride-depleted thylakoid membranes

Abstract

Chloride-depleted thylakoid membranes which are unable to catalyze the oxidation of water can nonetheless catalyze the oxidation of hydrogen peroxide (Kelly, P. and Izawa, S. (1978) Biochim. Biophys. Acta 502, 198-210). Using steady-state kinetic analyses, the inhibition of hydrogen peroxide oxidation by Tris, other amines, F- has been further examined in chloride-depleted thylakoid membranes. Based on these investigations, we conclude that inhibitions of H2O2 oxidation produced by such reagents are unrelated to their inhibitory activities on the photosynthetic oxygen-evolving complex which are observed when water is the substrate (Sandusky, P.O. and Yocum, C.F. (1984) Biochim. Biophys. Acta 766, 603-611; Sandusky, P.O. and Yocum, C.F. (1986) Biochim. Biophys. Acta 849, 85-93). Experiments using the ionophore A23187 along with exogenously added Mn2+ indicate that hydrogen peroxide oxidation by chloride-depleted thylakoids is catalyzed by a pool of free or loosely bound Mn. Further, EPR measurements indicate that the presence of hydrogen peroxide, under the assay conditions employed in our experiments, release Mn from the oxygen-evolving complex in chloride-depleted membranes. It is therefore this amine-sensitive pool of loosely bound Mn that is responsible for catalysis of H2O2 photooxidation in chlrodie-depleted thylakoids.