Properties of Adenosinetriphosphatase in Chromatophores and in Coupling Factor from the Photosynthetic Bacteria Cromatium Strain D

Chromatophores obtained from the photosynthetic bacteria Chromatium strain D catalyzed Mg²⁺ and Ca²⁺‐dependent ATP hydrolysis. The rate of ATPase activity was lower than the rate of photophosphorylation. Tryptic digestion of the Chromatophores activated both Mg²⁺‐ and Ca²⁺‐dependent ATPase activities while inhibiting only 15% of the phosphorylation. Incubation of the Chromatophores in a low salt medium (5 mM tricine‐NaOH), followed by centrifugation, yielded resolved Chromatophores which completely lost their capacity for photophosphorylation and most of their Mg²⁺‐ and Ca²⁺‐dependent ATPase activities. Incubation of the resolved particles with the supernatant fluid obtained after centrifugation, in the presence of Mg²⁺, restored photophosphorylation and ATPase activity. The soluble fraction (the crude coupling factor) had a low Mg²⁺‐ and Ca²⁺‐dependent ATPase activities. Both ATPase activities in the crude coupling factor could be activated by trypsin and inhibited by N,N′‐dicyclohexylcarbodiimide. There was a distinct difference in the requirements for ATP and cations between the membrane‐bound and the soluble ATPase The effect of the changes in the environment on the mode of binding of the substrate to the enzyme is discussed.