Quantitative determination of coupling factor CF1 of chloroplasts

Repeated washes of isolated chloroplasts with dilute sodium pyrophosphate solution results in the removal of carboxydismutase and some minor proteins from the thylakoid membranes. A subsequent treatment of the membranes with hypertonic sucrose solution yields pure coupling factor CF₁ in the supernatant. Purity of the protein was demonstrated by disc electrophoresis.The amount of CF₁ protein liberated was quantitatively determined. The percentage of CF₁ removed by this treatment was calculated from the Ca²⁺-dependent ATPase activity retained at the thylakoid membranes. From these data the total CF₁ content of chloroplasts was calculated. An average value of 0.42 mg CF₁ protein/mg chlorophyll was obtained. Based on a molecular weight for CF₁ of 326000 (see Farron, F. (1970) Biochemistry 9, 3823–3828), a ratio of 1 mole CF₁ per 860 moles chlorophyll was computed.