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Light Activation of Mg²⁺-dependent Adenosine 5'-Triphosphatase in Isolated Euglena Chloroplasts ¹

^a Department of Biochemistry, North Carolina State University, Raleigh, North Carolina 27607

Enhancement of Mg²⁺-dependent ATPase activity in Euglena gracilis chloroplasts by light in the presence of a sulfhydryl compound has been demonstrated. A number of uncouplers and energy transfer inhibitors were studied for their effects on the light enhancement of ATPase activity simultaneously with their effects on photophosphorylation. Results suggest that the light-enhanced ATPase activity in Euglena chloroplasts is an energy-initiated process and that the energy is supplied through electron flow upon illumination of the chloroplasts. However, by studying the difference in their response toward the various uncouplers and inhibitors, it seems that the two processes (photohydrolysis of ATP and photophosphorylation) share only the latter part of their energy-transferring pathway.