Participation of three distinct active states of chloroplast ATPase complex CF0 X CF1 in the activation by light and dithiothreitol.

Chloroplast ATPase complex (CF0 X CF1) in thylakoids is activated by illumination in the presence or absence of dithiothreitol or by incubation with both dithiothreitol and Pi in the post-illumination dark. The activation by dithiothreitol and Pi is inhibited by ADP and decreases with increasing time interval between the end of illumination and the addition of dithiothreitol and Pi. The dithiothreitol/Pi-activated ATP hydrolysis is highly sensitive to pH. The ATP hydrolysis activated by illumination in the presence of dithiothreitol decreases its sensitivity to stimulation by NH4Cl and increases its sensitivity to pH, with increasing time interval between the end of illumination and the addition of ATP. Its pH dependence approaches that of the dithiothreitol/Pi-activated ATP hydrolysis. These results suggest that in the post-illumination dark, the light/dithiothreitol-activated CFo X CF1 converts its state from the one (E2) which is sensitive to an uncoupler and relatively insensitive to pH to the one (E2i) which is insensitive to an uncoupler and highly sensitive to pH. In the post-illumination dark, the presence of both dithiothreitol and Pi brings about the activation of CFo X CF1 to E2i.