Inhibition of Photosynthetic Energy Conversion by Cupric Ion

Abstract

This study describes a specific Cu2+ and Ught-dependent inhibition of spinach (Spinaca oIracea L.) chloroplast reactions involving coupling factor 1 function. A primary effect is an inhibition of photopbosphorylation induced by illumination of Class II chloroplasts with micromolar Cu+ and pyocyanine in the absence of ADP, Mg2+, and HP042-. The inibition, which is dependent on free Cu2+ as indicated by protection by ethylene diamine tetraacetic acid and dithiothrsitol, requires ilumination (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 02independent oxidation of sulihydryl groups on coupling factor 1, which are essential to cataltic function. This conclusion is supported by the reduction of energy-dependent 3H-N-ethylmalsimide labelng of the y subunit ofcoupling factor 1 by the Cu2t-light pretreatment.