Inhibition of Photosynthetic Energy Conversion by Cupric Ion

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Abstract
A specific Cu2+ and light-dependent inhibition of spinach (Spinacia oleracea L.) chloroplast reactions involving coupling factor 1 function is described. A primary effect is an inhibition of photophosphorylation induced by illumination of class II chloroplasts with .mu.M Cu2+ and pyocyanine in the absence of ADP, Mg2+ and HPO42-. The inhibition, which is dependent on free Cu2+ as indicated by protection by EDTA and dithiothreitol, requires illumination (electron flow) for establishment of the specific inhibition to be noted. Protection is afforded by uncouplers and some partial protection is provided by .mu.M concentrations of ADP and ATP. Apparently Cu2+ causes an O2-independent oxidation of SH groups on coupling factor 1, which are essential to catalytic function. This is supported by the reduction of energy-dependent 3H-N-ethylmaleimide labeling of the .gamma. subunit of coupling factor 1 by the Cu2+-light pretreatment.