Gerratana B, Frey P A, Cleland W W
Institute for Enzyme Research, Department of Biochemistry, College of Agricultural Life Sciences, 1710 University Avenue, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA.
Biochemistry. 2001 Mar 6;40(9):2972-7. doi: 10.1021/bi002557x.
The transition-state structure for the reaction catalyzed by kanamycin nucleotidyltransferase has been determined from kinetic isotope effects. The primary (18)O isotope effects at pH 5.7 (close to the optimum pH) and at pH 7.7 (away from the optimum pH) are respectively 1.016 +/- 0.003 and 1.014 +/- 0.002. Secondary (18)O isotope effects of 1.0033 +/- 0.0004 and 1.0024 +/- 0.0002 for both nonbridge oxygen atoms were measured respectively at pH 5.7 and 7.7. These isotope effects are consistent with a concerted reaction with a slightly associative transition-state structure.
通过动力学同位素效应确定了卡那霉素核苷酸转移酶催化反应的过渡态结构。在pH 5.7（接近最佳pH）和pH 7.7（远离最佳pH）时的一级（¹⁸）O同位素效应分别为1.016±0.003和1.014±0.002。在pH 5.7和7.7时，两个非桥连氧原子的二级（¹⁸）O同位素效应分别测得为1.0033±0.0004和1.0024±0.0002。这些同位素效应与具有轻微缔合过渡态结构的协同反应一致。
