The Involvement of Sulphydryl Group of Coupling Factor 1 (CF1) in Energy Transduction in Chloroplast

Abstract

Both the control and chemically modified spinach thylakoid membranes were labelled with [14C]-ADP to study the energy dependent release of adenine nucleotide from coupling factor 1 (CF1). The photophosphorylation coupled to electron transport from water to methyl viologen was carried out under the same conditions as used for light-induced release of [14C]-ADP, except that cold ADP was present. The alkylation of the -SH group of salt-washed thylakoid membrane by n-ethylmaleiimide (NEM) resulted in a 17 per cent decrease in the energy dependent release of [14C]-ADP and a 53 per cent decrease in the rate of photophosphorylation. Dithiothreitol (DTT) could not reverse the inhibition of these activities caused by NEM. On treatment of NEM-modified chloroplasts with increasing concentrations of iodosobenzoate (IBZ), a further decline in both the energy-dependent release of [14C]-ADP and ATP synthesis rate was observed. However, DTT could reverse the inhibition caused by IBZ. Our data show that thiol modulation of CF1 alters the activation process and consequently the catalytic function of CF1 in chloroplast.