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

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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.

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