Properties of ATPase Activity in Coupling Factor from Chromatium Strain D Chromatophores


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Coupling factor extracted from chromatophores of the photosynthetic bacteria Chromatium strain D was partially purified. The enzyme catalyzed ATPase activity in the presence of Ca2+ and Mg2+ ions. Higher Vapp values were obtained when the activity was measured as a function of the divalent cation‐ATP complex rather than as a function of either the divalent cation or ATP because the free components competitively inhibited the activity in the presence of the cation‐ATP complex. The Km values were lower than or equal to the Ki values for free ATP indicating that the cation‐ATP complex is bound tighter than the free ATP to the enzyme. Based on these results a possible mode of binding of substrate to the active site of the enzyme was suggested. A comparative study indicated no changes in the temperature dependance of ATPase activity when the enzyme was solubilized. However, possible conformation changes could have caused a decrease in the Km values for the (Ca‐ATP)2− and (Mg‐ATP)2− and in the Ki for free Mg2+ ions and ATP. The Ki for free Ca2+ ions increased on solubilization of the coupling factor. ATPase activity was inhibited by dicyclohexylcarbodiimide both in the soluble and in the membrane‐bound coupling factor.

Original languageEnglish
Pages (from-to)463-469
Number of pages7
JournalEuropean Journal of Biochemistry
Issue number3
StatePublished - Apr 1977


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