Partial Resolution of the Enzymes Catalyzing Photophosphorylation: XIII. PROPERTIES OF ISOLATED SUBUNITS OF COUPLING FACTOR 1 FROM SPINACH CHLOROPLASTS

Abstract

Abstract 1. The subunits of coupling factor 1 from spinach chloroplasts have been isolated and their amino acid composition determined. 2. Antibodies to each subunit have been prepared and their effects on reactions involving coupling factor 1 have been studied. Antibodies against the 59,000 and 37,000 molecular weight subunits (α and γ components) inhibited cyclic photophosphorylation, phosphorylation coupled to the Hill reaction, and light-triggered Mg++-adenosine triphosphatase. Anti-α also inhibited the stimulation of H+ uptake in chloroplasts by ATP. 3. Antibodies against the two larger subunits (α and β) agglutinated chloroplast particles; the antibodies against the smaller subunits did not. 4. None of the antibodies against the subunits inhibited the ATPase activity of activated chloroplast coupling factor 1 (CF1) significantly when added singly. However, a combination of anti-α and anti-γ inhibited to the same extent as antibody against native CF1. 5. It is concluded that the α and γ subunits of CF1 are intimately involved in the function of the coupling factor. The e subunit is a regulatory subunit of the enzyme and the question is raised whether δ is also a regulatory subunit or a tightly bound contaminant of the enzyme.