Partial Resolution of the Enzymes Catalyzing Photophosphorylation: V. Interaction of Coupling Factor 1 from Chloroplasts with Ribonucleic Acid and Lipids

Abstract

Abstract 1. A crude extract of chloroplasts protected coupling factor 1 from chloroplasts (CF1) against heat inactivation at 64°. Two components present in crude extracts appeared to contribute to this stabilization. Polynucleotides as well as lipids purified from chloroplast extracts conferred heat stability on CF1. 2. RNA from various sources substituted for chloroplast RNA, but distinct differences in effectiveness were noted. No protection was observed either with RNA digested with RNase or with native or denatured DNA. Relatively high concentrations of polycytidylic acid, but not of polyadenylic acid or polyuridylic acid, conferred heat stability. At very high concentration (5 mm) nucleoside triphosphates protected, CTP and UTP being much more effective than the other nucleotides tested. 3. In contrast to RNA, which protected both CF1 and the heat-activated ATPase, the protection by lipids was much more pronounced with CF1 than with ATPase. Moreover, lipids but not RNA protected CF1 against cold inactivation. Dithiothreitol-activated ATPase of CF1 was slightly stimulated by lipids. 4. These findings pointed strongly to a lipid component in the chloroplast membrane as one of the reactants with CF1. They suggested, furthermore, that another component must be responsible for the masking of ATPase activity observed with chloroplast particles.