Klemme J H, Gest H
Proc Natl Acad Sci U S A. 1971 Apr;68(4):721-5. doi: 10.1073/pnas.68.4.721.
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.
在深红红螺菌中，细胞质和膜部分均观察到无机焦磷酸酶活性。可溶性酶约占粗提物中总活性的80%，是本报告的研究对象。该酶的活性和稳定性均需要Zn(2+)，其分子量约为90,000（凝胶过滤测定）。底物是MgP₂O₇²⁻，游离焦磷酸（P₂O₇⁴⁻）是一种强抑制剂。动力学实验表明底物结合位点之间存在同促相互作用；这些相互作用受作为激活剂的Mg(2+)影响。在低浓度的Zn(2+)下，焦磷酸酶被NADH、NADPH和MgATP抑制；在0.4 - 0.7 mM时发生50%的抑制。高浓度的Zn(2+)（10⁻⁴ - 10⁻³ M）可逆转这些效应。核苷酸似乎通过影响Zn(2+)结合来抑制“天然”酶的活性。深红红螺菌的这种酶似乎是第一个已知的受变构调节的细菌无机焦磷酸酶实例。
