Multiple Isotope Effects on Enzyme-Catalyzed Reactions

Isotope effects have long been popular as a method for studying mechanisms of chemical reactions (1, 2). Application of this method to enzymatic reac­tions has come slowly, in part because of the difficulty of making measurements of the necessary precision, and in part because of the difficulty of interpreting the variations in rate that occur in multistep reactions. The theory and practice of isotope effects has now reached the stage where a variety of interesting mechanistic studies are possible (3-9), including use of heavy­ atom isotope effects (5), application to multireactant enzymes (9a, 10), pH dependence of isotope effects (11, 12), proton inventory studies (9), relative deuterium and tritium isotope effects (13), the remote label method (14), and the use of deuterium and tritium isotope effects for the study of tunneling (J. Klinman, personal communication).