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Velázquez, I; Celis, H; Romero, I (1993)

REGULATION OF DIVALENT CATIONS OF THE MEMBRANE-BOUND PYROPHOSPHATASE OF RHODOSPIRILLUM RUBRUM, AS SHOWN BY THE HYDROLYSIS OF TRIPOSITIVE-PYROPHOSPHATE COMPLEXES

Biometals 6(3):143-148
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Tripositive-pyrophosphate [M(III)-PPi] complexes were used to investigate the role of free divalent cations on the membrane-bound pyrophosphatase. Divalent cations remain free and the M(III)-PPi complexes were employed as substrates. Formation of a La-PPi complex was studied by fluorescence, and the fact that Zn2+ and Mg2+ remain free in the solution was validated. Hydrolysis of La-PPi is stimulated by the presence of fixed concentrations of free Mg2+ or Zn2+ and this stimulation depends on the concentration of the cations when the La-PPi complex is fixed. The divalent cation stimulation order is Zn2+ > Co2+ > Mg2+ > Mn2+ > Ca2+ (at 0.5 m m of free cation). With different M(III)-PPi complexes, Zn2+ produces the same Km, for all the complexes and Mg2+ stimulates with a different Km. The results suggest that both Mg2+ and Zn2+ activate the membrane-bound pyrophosphatase but through different mechanisms. © 1993 Rapid Communications of Oxford Ltd.