Abstract

There has been a considerable amount of controversy concerning the ability of photosystem II to evolve oxygen in the absence of the 33-kDa, manganese-stabilizing protein. Early reports indicated that some capacity for oxygen evolution existed in manganese-stabilizing protein-depleted membranes while more recent studies have suggested that the observed oxygen evolution activity arose from residual manganese-stabilizing protein present in the salt-washed preparations. In this paper, it is conclusively demonstrated that significant rates of steady-state oxygen evolution are observed in oxygen-evolving photosystem II membranes in the absence of detectable quantities of the manganese-stabilizing protein. More then 99% of the manganese-stabilizing protein was removed by either one CaCl2 or two NaCl-urea washes. The amount of manganese-stabilizing protein removed was quantified immunologically using mouse polyclonal antibodies. Oxygen evolution rates of 115-140 mumol of O2 (mg of Chl)-1 h-1 were observed in the NaCl-urea-washed preparations. These rates represent about 24% of the rate observed in untreated membranes [450-600 mumol of O2 (mg of Chl)-1 h-1]. Somewhat lower, although still significant rates were observed in the CaCl2-washed preparations. Optimal rates of oxygen-evolving activity in NaCl-urea-washed membranes which are devoid of the manganese-stabilizing protein required high concentrations of calcium and chloride.