| Abstract: | A soluble inorganic pyrophosphatase from photolithoautotrophically grown Rhodopseudomonas palustris was purified to a state of apparent homogeneity applying high resolving liquid chromatography steps. Values of 65 500 and 64 500 were calculated for the relative molecular mass under non-dissociating conditions employing gel filtration and high-performance liquid chromatography, respectively. Dissociation sodium dodecyl sulfate gel electrophoresis resulted in a value of 32 000, indicating that the enzyme is composed of two subunits of equal molecular mass. Isoelectric focusing revealed a pI value of 4.7. The purified enzyme was specific for PPi and the activity was modified by divalent cations. Ca2+, Mn2+, Mg2+ and Co2+ were potent activators at a concentration ratio of [Me2+]/[PPi] less than 1. Ca2+ turned out to be the most potent activator. Free Me2+ was inhibitory on the PPiase activity. The (Me-PPi) complex is regarded as the functional substrate. Km and Ki values of the metal activation and inhibition were determined. An activation energy of Ea = 14.4 kJ/mol was derived from Arrhenius plots for the enzymatic reaction. |
