Steady-state kinetics nomenclature

At this point, we may note that the most immediate characteristic of an overall solvent isotope effect on steady-state kinetic parameters, kwonlkoon, Vmoh/ Food, or (F/i0HOH/ F/K)DOD, is its direction. The customary nomenclature attributes a normal solvent isotope effect when the kinetic parameters are larger in HOH, and an inverse solvent isotope effect when the kinetic parameters are larger in DOD. Solvent isotope effects can also be primary and secondary. 

Enzymes are biocatalysts, as such they facilitate rates of biochemical reactions. Some of the important characteristics of enzymes are summarized. Enzyme kinetics is a detailed stepwise study of enzyme catalysis as affected by enzyme concentration, substrate concentrations, and environmental factors such as temperature, pH, and so on. Two general approaches to treat initial rate enzyme kinetics, quasi-equilibrium and steady-state, are discussed. Cleland s nomenclature is presented. Computer search for enzyme data via the Internet and analysis of kinetic data with Leonora are described. 

TABLE 11.5 Cleland nomenclature for bisubstrate reactions exemplified. Three common kinetic mechanisms for bisubstrate enzymatic reactions are exemplified. The forward rate equations for the order bi bi and ping pong bi hi are derived according to the steady-state assumption, whereas that of the random bi bi is based on the quasi-equilibrium assumption. These rate equations are first order in both A and B, and their double reciprocal plots (1A versus 1/A or 1/B) are linear. They are convergent for the order bi bi and random bi bi but parallel for the ping pong bi bi due to the absence of the constant term (KiaKb) in the denominator. These three kinetic mechanisms can be further differentiated by their product inhibition patterns (Cleland, 1963b)... 

The velocity equations for bisubstrate and trisubstrate reactions are usually formidable if expressed in terms of individual rate constants, especially in the steady-state treatment. The resulting equations are almost useless until the rate constants are grouped into relatively simple kinetic constants that can be experimentally determined (Chapter 4). Various methods for grouping the individual rate constants have been developed by Alberty (1953), DaMel (1957), Bloomfield et al. (1962), Wong Hanes (1962), Cleland (1963), Mahler Cordes (1966), Segel (1975), and others. The nomenclature of Cleland is now in general use. 

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