Interference of methyl trachyloban-19-oate ester with CF0 of spinach chloroplast H+-ATPase

In isolated spinach chloroplasts, low concentrations (I50=14 μM) of methyl trachyloban-19-oate ester inhibited ATP synthesis and coupled electron transport as well as light-activated membrane-bound Mg2+-ATPase activity. Basal (-Pi) and uncoupled electron transport and heat-activated Ca2+-dependent ATPase activity of isolated coupling factor proteins were unaffected by methyl trachyloban-19-oate. Thylakoids partially stripped of coupled factor by EDTA were unable to accumulate protons in the light. However, increasing concentrations of methyl trachyloban-19-oate ester restored this ability. It is concluded that the methyl trachyloban-19-oate ester effects result from blocking proton transport through the CF0 channel. Methyl trachyloban-19-oate ester exhibited non-competitive kinetics with DCCD and triphenyltin. These results suggest that the natural products, DCCD and triphenyltin, access inhibition sites in CF0. The Ki is 75 μM.