title: Kinetic characterization and partial purification of the membrane-bound inorganic pyrophosphatase from Rhodopseudomonas palustris.
abstract: A membrane-bound inorganic pyrophosphatase from Rhodopseudomonas palustris has been studied by kinetic analysis. The enzymatic activity was stimulated by Mg2+, and the (Mg-PPi) complex is regarded to be the functional substrate. Free Mg2+ revealed a significant influence on the membrane-bound PPiase activity. Kinetic data were determined at various fixed concentrations of free Mg2+. Mg2+ is proposed to act as an activator in two ways. It may interact with the enzyme directly, and may combine with PPi to yield the functional substrate Mg-PPi. Ca2+ revealed a non-competitive type of inhibition on the Mg2+-activated enzyme. The membrane-bound PPiase activity was firmly attached to the chromatophore membrane. To achieve an almost entire solubilization, both, Triton X-100 and high concentrations of Mg2+, had to be applied. An enrichment method along with stepwise lowering the concentrations of Triton X-100 and Mg2+ after the solubilization has been established. The solubilized and partially purified enzyme was stimulated by phospholipids while the influence of free Mg2+ was lost. Three different energies of activation as a function of temperature were derived from Arrhenius plots for the membrane-bound as well as for the solubilized PPiase activity.
mesh_terms: D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D006358:Hot Temperature; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D010743:Phospholipids / Q000502:physiology; D011755:Pyrophosphatases / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D012241:Rhodopseudomonas / Q000201:enzymology*; D012995:Solubility; D013816:Thermodynamics
chemical_list: D010743:Phospholipids; D011755:Pyrophosphatases; D008274:Magnesium; D002118:Calcium