Partial Resolution of the Enzymes Catalyzing Photophosphorylation: IV. Interaction of Coupling Factor 1 from Chloroplasts with Components of the Chloroplast Membrane

Abstract

Abstract 1. A DEAE-Sephadex chromatography step was introduced in the purification of the latent ATPase from chloroplasts (chloroplast coupling factor (CF1)). On elution an inactive protein was obtained, which was reactivated on storage in 2.0 m ammonium sulfate containing 2 mm ATP. 2. Treatment of tritium-labeled acetyl-CF1 with trypsin or heat activated the Ca++-dependent ATPase, but abolished the capacity of CF1 to combine with resolved chloroplast particles. 3. It was shown with tritium-labeled CF1 that a divalent cation such as Mg++ or Ca++ was required for the binding of the protein to the chloroplast membrane. 4. Combination of CF1 with the chloroplast membrane resulted in an increase in the cold stability of the protein. This allotopic property was used as an additional assay for the interaction between CF1 and the membrane. 5. On extraction of chloroplasts with solvents, two fractions, one soluble and one insoluble, were separated. Both were required for the reconstitution of particles that were capable of combining with CF1.