title: Characterization of the membrane-bound inorganic pyrophosphatase in Rhodospirillum rubrum.
abstract: The membrane-bound inorganic pyrophosphatase (EC 3.6.1.1) from Rhodospirillum rubrum has been investigated with the tools of enzyme kinetics, and with two amino acid reagents, N-ethyl-maleimide (MalNET) and 4-chloro-7-nitrobenzofurazan (Nbf-Cl). 1. The concentration of the true substrate, MgPPi, was varied with constant concentrations of free Mg2+ or PPi. It was observed that Mg2+ acted as an activator. 2. Heat inactivation of the enzyme at 62 degrees C was slowed down in the presence of Mg2+. 3. MalNET and Nbf-Cl bind to the enzyme, and inhibit its activity. The effect of both reagents is dependent on the temperature. 4. A model is proposed where the 1:1 complex of Mg2+:PPi acts as substrate and Mg2+ interacts directly with the enzyme as an activator. PPi can bind to the enzyme, but is not hydrolyzed in the uncomplexed form.
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology*; D011756:Diphosphates; D005033:Ethylmaleimide / Q000494:pharmacology; D006358:Hot Temperature; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D011755:Pyrophosphatases / Q000302:isolation & purification*; D012247:Rhodospirillum rubrum / Q000201:enzymology*
chemical_list: D011756:Diphosphates; D011755:Pyrophosphatases; D009327:4-Chloro-7-nitrobenzofurazan; D008274:Magnesium; D005033:Ethylmaleimide