A method was found for the in situ activation of the latent Ca2+-ATPase of the coupling factor from chloroplasts of Euglena gracilis and its resultant solubilization. The activation causes the concomitant solubilization of the enzyme and facilitates easy and nearly complete extraction. The activation consists of lowering the pH of isolated chloroplasts for 2 minutes to pH 4.5 to 4.7 with acetic acid, followed by neutralization. Increases in activity as high as 18-fold can be obtained. The method does not appear to work with chloroplasts from other sources.
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