REGULATION OF DIVALENT-CATIONS OF THE MEMBRANE-BOUND PYROPHOSPHATASE OF RHODOSPIRILLUM-RUBRUM, AS SHOWN BY THE HYDROLYSIS OF TRIPOSITIVE-PYROPHOSPHATE COMPLEXES
I. Velazquez et al., REGULATION OF DIVALENT-CATIONS OF THE MEMBRANE-BOUND PYROPHOSPHATASE OF RHODOSPIRILLUM-RUBRUM, AS SHOWN BY THE HYDROLYSIS OF TRIPOSITIVE-PYROPHOSPHATE COMPLEXES, BioMetals, 6(3), 1993, pp. 143-148
Tripositive-pyrophosphate [M(III)-PPi] complexes were used to investig
ate the role of tree divalent cations on the membrane-bound pyrophosph
atase. Divalent cations remain free and the M(III)-PPi complexes were
employed as substrates. Formation of a La-PPi complex was studied by f
luorescence, and the fact that Zn2+ and Mg 2+ remain free in the solut
ion was validated. Hydrolysis of La-PPi is stimulated by the presence
of fixed concentrations of free Mg2+ or Zn2+ and this stimulation depe
nds on the concentration of the cations when the La-PPi complex is fix
ed. The divalent cation stimulation order is Zn2+ > Co2+ > Mg2+ > Mn2 > Ca2+ (at 0.5 mm of free cation). With different M(III)-PPi complexe
s, Zn2+ produces the same K(m) for all the complexes and Mg2+ stimulat
es with a different K(m). The results suggest that both Mg2+ and Zn2activate the membrane-bound pyrophosphatase but through different mech
anisms.