The Quasi-Equilibrium Approximation Enzymatic Reaction Kinetics

2 The Quasi-Equilibrium Approximation Enzymatic Reaction Kinetics 

Let us refer again to kinetic scheme (2.8) describing the consecutive reaction with the first step being reversible. If the equilibrium described by the constants k and k2 is established quickly, i.e. the step resulting in the end product is slow, the quasiequilibrium principle is applicable in this case. According to this principle, the concentration of intermediate B practically does not differ from its equilibrium value owing to the hard-to-disturb equilibrium and can be expressed in terms of the ratio of the constants ki and k2 

the quasi-equilibrium principle should be obeyed provided the condition ki -C k2 is met. The corresponding calculation (Fig. 2.23) confirms this assumption. 

The quasi-equilibrium principle gained a widespread practical use in enzyme kinetics, a branch of chemical kinetics describing catalytic reactions involving 

E is an enzyme, 5 is a reactant (a substrate), E is a reaction product, ES is an enzyme-substrate complex. The process provides for reversible ES formation followed by its decay into the reaction product with simultaneous enzyme regeneration. Provided the step of product formation is slow (kz -i), the reaction kinetics can be described in the framework of the quasi-equilibrium principle. 

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