Inhibition of Photosynthetic Energy Conversion by Cupric Ion

Abstract

This study describes a specific Cu(2+) and light-dependent inhibition of spinach (Spinacia oleracea L.) chloroplast reactions involving coupling factor 1 function. A primary effect is an inhibition of photophosphorylation induced by illumination of Class II chloroplasts with micromolar Cu(2+) and pyocyanine in the absence of ADP, Mg(2+), and HPO(4) (2-). The inhibition, which is dependent on free Cu(2+) as indicated by protection by ethylene diamine tetraacetic acid and dithiothreitol, requires illumination (electron flow) for establishment of the specific inhibition to be noted. Protection is also afforded by uncouplers and some partial protection is provided by micromolar concentrations of ADP and ATP. The data strongly suggest that Cu(2+) causes an O(2)-independent oxidation of sulfhydryl groups on coupling factor 1, which are essential to catalytic function. This conclusion is supported by the reduction of energy-dependent (3)H-N-ethylmaleimide labeling of the gamma subunit of coupling factor 1 by the Cu(2+)-light pretreatment.