Characterization of the Transition-State Structure of the Reaction of the Reaction of Kanamycin Nucleotidyltransferase by Heavy-Atom Kinetic Isotope Effects

摘要

The transition-state structure for the reaction catalyzed by kanamycin nucleotidyltransferase las been determined from kinetic isotope effects. The primary 180 isotope effects at pH 5.7 (close to the )ptimum pH) and at pH 7.7 (away from the optimum pH) are respectively 1.016+-0.003 and 1.014+-).002. Secondary 180 isotope effects of 1.0033+-0.0004 and 1.0024+-0.0002 for both nonbridge oxygen ltoms were measured respectively at pH 5.7 and 7.7. These isotope effects are consistent with a concerted 'eactiQn with a slightly assQciatiye transition-state structure.