Nomenclature bisubstrate reactions

TABLE 7.2. Cleland Nomenclature for Bisubstrate Reactions Exemplified ... 

Examples of the bisubstrate reactions according to Cleland nomenclature are listed in Table 7.2. 

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)... 

This nomenclature has been introduced by Cleland (1963), but other descriptions of bisubstrate mechanisms are also found in the biochemical literature. For example, a sequential addition in bisubstrate reactions, an Ordered Bi Bi mechanism is also called a compulsory-order ternary-complex mechanism whereas a Random Bi Bi mechanism is called a random-order ternary-complex... 

The nomenclature of Cleland is very versatile and can be applied to even more complex inhibition patterns that occur in double reciprocal plots. In addition, the nomenclature of Cleland is also applicable to double reciprocal plots for bisubstrate and tiisubstrate reactions, in the absence and in the presence of the products of reaction, which makes this nomenclamre even more versatile. 

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. 

In bisubstrate enzyme reactions, an effort must be made to reduce the complexity of kinetic expression. Therefore, and according to the nomenclature of Northrop (1977), we shall write the conventional expression for an isotope effect, as... 

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