Enhancement of Adenosine Triphosphatase Activity of Purified Chloroplast Coupling Factor 1 in an Aqueous Organic Solvent

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The ATPase activity of purified coupling factor 1 (CF₁) of spinach chloroplasts [EC 3. 6. 1. 3] was reversibly enhanced in some aqueous organic solvents, notably methanol, ethanol, and acetone. Pretreatment of CF₁ with 20% (v/v) methanol did not affect the subsequent activity. The activity depended entirely on the final concentration of methanol in the reaction mixture. In the presence of 20%. methanol, the K_m of Ca²⁺-ATPase for ATP was lowered from 0.4mM to 0.2mM. Not only Ca²⁺, but also Cd²⁺, Mg²⁺, Mn²⁺, and Zn²⁺ supported the ATPase activity at rates of higher than 7 μmol•mg protein^-1•min^-1• Co²⁺, Ni²⁺, and Pb²⁺ supported the activity at rates of 0.5-1.0 μmol•mg protein^-1•min^-1. The activities supported by the following cations, if any, were less than 0.2 μmol•mg protein^-1•min^-1; Ba²⁺ Cu²⁺ Fe²⁺ Hg²⁺, Sn²⁺, and Sr²⁺. The optimum concentration of methanol for Ca²⁺-ATPase and Mg²⁺-ATPase activities was about 30% (v/v). The optimum pH values for Ca²⁺-ATPase and Mg²⁺-ATPase activities were about 8.0 and 8.8, respectively.
The enhancing effect of organic solvents appears to be associated with their relative lipophilic character as defined by the octanol-water partition coefficient.
The Ca²⁺-ATPase activities of the trypsin-activated and the heat-activated CF₁ were inhibited and their Mg²⁺-ATPase activities were enhanced by the presence of methanol in the reaction mixture.