title: Regulatory properties of an inorganic pyrophosphatase from the photosynthic bacterium Rhodospirillum rubrum.
abstract: In Rhodospirillum rubrum, inorganic pyrophosphatase activity is observed in both the cytoplasmic and membrane fractions. The soluble enzyme accounts for about 80% of the total activity in crude extracts, and is the subject of this report. Zn(2+) is required for both activity and stability of the enzyme, which has a molecular weight of approximately 90,000 (gel-filtration determinations). The substrate is MgP(2)O(7) (2-), and free pyrophosphate (P(2)O(7) (4-)) is a strong inhibitor. Kinetic experiments indicate homotropic interactions between substrate-binding sites; these interactions are influenced by Mg(2+), which is an activator. At low concentrations of Zn(2+), the pyrophosphatase is inhibited by NADH, NADPH, and MgATP; 50% inhibition occurs at 0.4-0.7 mM. These effects are reversed by high concentrations of Zn(2+) (10(-4)-10(-3) M). The nucleotides appear to inhibit activity of the "native" enzyme through an effect on Zn(2+) binding. The R. rubrum enzyme seems to be the first known example of a bacterial inorganic pyrophosphatase subject to allosteric regulation.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D001665:Binding Sites; D002474:Cell-Free System; D011756:Diphosphates / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009243:NAD / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology; D010084:Oxidation-Reduction; D011755:Pyrophosphatases / Q000032:analysis / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012246:Rhodospirillum / Q000201:enzymology*; D015032:Zinc / Q000494:pharmacology
chemical_list: D011756:Diphosphates; D009243:NAD; D009249:NADP; D000255:Adenosine Triphosphate; D011755:Pyrophosphatases; D008274:Magnesium; D015032:Zinc