Inhibition of Photosynthetic Energy Conversion by Cupric Ion : EVIDENCE FOR Cu-COUPLING FACTOR 1 INTERACTION

This study describes a specific Cu²⁺ 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 Cu²⁺ and pyocyanine in the absence of ADP, Mg²⁺, and HPO₄²⁻. The inhibition, which is dependent on free Cu²⁺ 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 Cu²⁺ causes an O₂-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 ³H-N-ethylmaleimide labeling of the γ subunit of coupling factor 1 by the Cu²⁺-light pretreatment.