Stable isotopes can be a useful tool in studying the basic processes involved in enzymatic catalysis. Isotope effects are quantifiable values related to the substitution of isotopes. It derives from the difference in zero-point energies. In contrast to non-catalyzed reactions, enzyme-catalyzed reactions involve multiple steps, the overall isotope effects are the sum of the isotope effects in each step. There are two major kinds of isotope effects, equilibrium isotope effects (EIEs) and kinetic isotope effects (KIEs). Each of them can provide us insights into different states in the reaction. This thesis describes several researches related to using the stable isotopes to study microbial metabolism. It is demonstrated in Chapter 2 that a method is developed for the measurement of H isotope fractionation patterns in hydrogenases. After the development of the method, a detailed study of the H2 metabolism catalyzed by different hydrogenases is presented in Chapter 3. The methods developed in hydrogenase studies were deployed in nitric oxide reductase-catalyzed N2O production studies, which is described in Chapter 4.
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