Studies on the Hydrolysis of Adenosine Triphosphate by Spinach Chloroplasts.

During studies on photophosphorylation in cell-free preparations of the blue-green alga, Anabaena variabilis, a photohydrolysis of ATP was found to be induced by high concentrations of cysteine or GSH, while photophosphorylation became inhibited (1, 2). A similar photohydrolysis was also reported with chloroplasts from spinach leaves, but still higher sulfhydryl concentrations were required to inhibit ATP synthesis and to induce ATP hydrolysis. Both light-dependent reactions (2) required an electron carrier and Mg+f and both were inhibited by ammonium ions and n-butyl 3,5-diiodo-4-hydroxybenzoate. This report describes some additional characteristics of the light-dependent ATPase in spinach chloroplasts. The studies support the conclusion that ATP synthesis and hydrolysis in chloroplasts are closely interrelated and suggest that at least a part of the light-induced elect,ron transport pathway is common to both processes. During this study it was found that illumination of the system in the absence of ATP, followed by addition of the substrate in the dark, still resulted in ATP hydrolysis. The data suggest that an intermediate is generated in the light phase which supports ATP hydrolysis in the dark.