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. 1971 Apr;68(4):721–725. doi: 10.1073/pnas.68.4.721

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

Jobst-Heinrich Klemme 1,*, Howard Gest 1
PMCID: PMC389028  PMID: 4396317

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. 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 MgP2O72-, and free pyrophosphate (P2O74-) 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+ (10-4-10-3 M). 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.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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