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Activation of Coupling Factor 1 from Euglena gracilis Chloroplasts ¹

Conditions for Optimal Activation and Their Possible Physiological Significance

Department of Biochemistry, North Carolina State University, Raleigh, North Carolina 27695

The recently described method for the activation of the Ca²⁺-ATPase of coupling factor 1 from chloroplasts (CF₁) of Euglena gracilis by low pH occurs optimally in high concentrations of NaCl, and is unaffected by the acid used to lower the pH to 4.5. Activation is inhibited by light, and this effect can be reversed by the presence of NADP⁺, ADP + inorganic phosphate, or an uncoupler. There appears to be no difference between the activities in the soluble and the particulate phases, and they seem to represent the same enzyme. The response of the activation process to light and to effectors of electron transport and phosphorylation indicates a possible physiological role for the acid activation of Euglena CF₁.