Kasho V N, Baykov A A
Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
Biochem Biophys Res Commun. 1989 Jun 15;161(2):475-80. doi: 10.1016/0006-291x(89)92623-5.
A scheme of Mg2+ and Pi binding to yeast inorganic pyrophosphatase has been deduced from the concentration dependencies of the rate of oxygen exchange between Pi and water. The exchange reaction requires the binding of MgPi and free Pi (pathway I) or two MgPi (pathway II) in addition to two Mg2+ ions bound in the absence of Pi. Pathway II predominates above 0.16 mM Mg2+. The rate of formation of bound PPi from bound Pi for pathway II is three times as high as that for pathway I. The results suggest that the binding of the fourth Mg2+ ion to pyrophosphatase stimulates its synthetic vs its hydrolytic capability.
根据无机磷酸（Pi）与水之间氧交换速率的浓度依赖性，推导了镁离子（Mg2+）和Pi与酵母无机焦磷酸酶结合的模式。除了在无Pi时结合的两个Mg2+离子外，交换反应还需要MgPi和游离Pi的结合（途径I）或两个MgPi的结合（途径II）。在Mg2+浓度高于0.16 mM时，途径II占主导。途径II中从结合的Pi形成结合的焦磷酸（PPi）的速率是途径I的三倍。结果表明，第四个Mg2+离子与焦磷酸酶的结合增强了其合成能力而非水解能力。
