Hackney D D, Boyer P D
Proc Natl Acad Sci U S A. 1978 Jul;75(7):3133-7. doi: 10.1073/pnas.75.7.3133.
During the rapid exchange of oxygens of Pi with water catalyzed by yeast inorganic pyrophosphatase, Pi at the catalytic site may either dissociate or undergo reversible loss of an oxygen to water. The effective partitioning of bound Pi during exchange starting with medium Pi containing 18O in all four oxygens has been evaluated by mass spectral analysis of the change in the distribution of Pi species containing zero to four 18O oxygens per Pi. This analysis indicates that the rate of Pi release from the enzyme is only 1.4 times faster than the rate of reformation of the anhydrous intermediate. A similar partitioning of bound Pi is observed during PPi hydrolysis, indicating that hydrolysis and medium exchange have common intermediates. The approach should be applicable to study of related phosphate oxygen exchanges.
在酵母无机焦磷酸酶催化下Pi与水的氧快速交换过程中，催化位点的Pi可能解离，也可能与水发生氧的可逆损失。从所有四个氧均含18O的介质Pi开始交换时，通过对每个Pi含零至四个18O氧的Pi物种分布变化进行质谱分析，评估了结合Pi的有效分配情况。该分析表明，Pi从酶上释放的速率仅比无水中间体重新形成的速率快1.4倍。在PPi水解过程中观察到结合Pi的类似分配情况，表明水解和介质交换有共同中间体。该方法应适用于相关磷酸氧交换的研究。
