Regulatory Properties of an Inorganic Pyrophosphatase from the Photosynthetic Bacterium Rhodospirillum rubrum

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 68; no. 4; pp. 721 - 725
• Main Authors: Klemme, Jobst-Heinrich, Gest, Howard
• Format: Journal Article
• Language: English
• Published: National Academy of Sciences of the United States of America 01.04.1971; National Acad Sciences
• Subjects: Biological Sciences: Biochemistry; Biosynthesis; Chromatophores; Enzymes; Kinetics; Molecular weight; Nucleotides; Ratios; Reaction kinetics; Reagents; Sulfates
• DOI: 10.1073/pnas.68.4.721
• ISSN: 0027-8424

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. Zn2+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 MgP2O7 2-, and free pyrophosphate (P2O7 4-) is a strong inhibitor. Kinetic experiments indicate homotropic interactions between substrate-binding sites; these interactions are influenced by Mg2+, which is an activator. At low concentrations of Zn2+, 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 Zn2+(10-4-10-3M). The nucleotides appear to inhibit activity of the ``native'' enzyme through an effect on Zn2+binding. The R. rubrum enzyme seems to be the first known example of a bacterial inorganic pyrophosphatase subject to allosteric regulation.