Reversible Conversion from Ca2+-ATPase Activity to Mg2+- and Mn2+-ATPase Activities of Coupling Factor Purified from Acetone Powder of Rhodospirillum rubrum Chromatophores1

Abstract

It is known that the coupling factor purified from the acetone powder of chromatophores from Rhodospirillum rubrum shows ATPase activity in the presence of Ca²⁺, but not in the presence of Mg²⁺ or Mn²⁺. The present study deals with conditions, under which the Ca²⁺-ATPase activity is reversibly converted into Mg²⁺- and Mn²⁺-ATPase activities with the purified coupling factor. 1. Of the pH indicators tested, 6 kinds converted the Ca²⁺-ATPase activity into Mg²⁺- and Mn²⁺-ATPase activities in the order, ethyl orange>tropaeolin 000;≥metanil yellow>tropaeolin 00>ethyl red;≥bromthymol blue. 2. Of the detergents tested, those other than Triton X-100 and Brij 58 caused the conversion described above; dodecylsulfonate was most effective, whereas dodecylpyridinium chloride was moderately effective. 3. 2,4-Dinitrophenol stimulated approximately two-fold the Ca²⁺-ATPase activity, but not the Mg²⁺- or Mn²⁺-ATPase activity at all. However, in the presence of dodecylpyridinium chloride, the pH indicator remarkably stimulated the Mg²⁺- and Mn²⁺-ATPase activities, accompanied with a partial inhibition of the Ca²⁺-ATPase activity. Methyl red and ethyl red showed similar effects. 4. All the nucleoside triphosphates tested can serve as the substrate. ATP was most effective for the Ca²⁺-ATPase activity, whereas dATP was most effective for the Mg²⁺- and Mn²⁺-ATPase activities induced by ethyl orange. 5. In the presence of ethyl orange, the ATPase activity was induced by various divalent cations in the following order of effectiveness, Mg²⁺>Zn²⁺>Co²⁺>Mn²⁺>Ni²⁺. 6. The mechanism of the reversible conversion from the Ca²⁺-ATPase activity to the Mg²⁺-and Mn²⁺-ATPase activities by pH indicators and detergents is discussed.