Inhibition by Triphenyltin Chloride of a Tightly‐Bound Membrane Component Involved in Photophosphorylation

Abstract

At very low concentrations (< 1 μM) triphenyltin chloride inhibits ATP formation and coupled electron transport in isolated spinach chloroplasts. Basal (−Pi) and uncoupled electron transport are not affected by triphenyltin. The membrane‐bound ATP ⇌ Pi exchange and Mg2+‐dependent ATPase activities of chloroplasts are also completely sensitive to triphenyltin, although the Ca2+‐ dependent and Mg2+‐dependent ATPase activities of the isolated coupling factor protein are insensitive to triphenyltin. The light‐driven proton pump in chloroplasts is stimulated (up to 60 %) by low levels of triphenyltin. Indeed, the amount of triphenyltin necessary to inhibit ATP formation or stimulate proton uptake is dependent upon the amount of chloroplasts present in the reaction mixture, with an apparent stoichiometry of 2 — 2.5 triphenyltin molecules/100 chlorophyll molecules at 50: