Binding of Cibacron blue F3GA to chloroplast coupling factor. Competitive inhibition of ATP synthesis and hydrolysis

Abstract

Photophosphorylation in spinach chloroplasts and the Ca 2+-ATPase activity of soluble coupling factor 1 (CF 1) were inhibited by Cibacron blue F3GA. The inhibition of the heat-activated ATPase of CF 1 was competitive with ATP while an allosteric effect was seen in dithioerythritol-activated CF 1 with a Hill coefficient of 1.6. The inhibition of photophosphorylation was competitive with ADP but not with P 1. The interaction between CF 1 and Cibacron F3GA induced a red shift in the spectrum of the dye. The stoicheiometry of the CF 1-dye complex calculated from the difference spectra was nearly 2 for native CF 1 and nearly 3 for activated CF 1. The difference spectra of the dye-CF 1 complex changed with time (hours). The changes with native CF 1 were larger in the trough (575–578 nm) and the dye became more tightly bound to CF 1 with time.