Inactivation and reactivation of light-triggered ATP hydrolysis on the chloroplast coupling factor

Decay of light-triggered ATP hydrolysis in the dark was diminished with a decrease in chloroplast concentration. The enhancing effect of NH₄Cl on ATP hydrolysis decreased with dark time. The decrease was much faster than that in ATP hydrolysis activity. The NH₄Cl effect increased with ATP preincubation time. Reactivation of ATP hydrolysis occurred with the progress of ATP hydrolysis. P_i enhanced the activation remarkably. These results suggest that ATP hydrolysis produces some energized state, which stimulates NH₄C1 effect and makes coupling factor active in the presence of P_i and that to keep coupling factor active, energy is not necessarily needed.