Use of the RLS Approximation

Let s illustrate how the RLS approximation can be used by deriving a rate equation for the disappearance of S, —rs, in the above reaction. We might be tempted to begin by writing 

The term (1) on the right-hand side of this equation results from the fact that 1 molecule of S is consumed each time that the RLS proceeds to the right, on a net basis. 

The rate equation contains the concentrations of two active centers, E-S and E-P. These concentrations must be written in terms of the concentrations of the reactants and products. To do this, we assume that Reactions (5-H) and (5-J) are in equilibrium and write the equihbiium expressions for these reactions. 

Use equilibrium expression to relate [active centers] to [reactants] and [products] 

K is the equilibrium constant for Reaction (5-H), based on concentration. As an aside, K is refrared to as a binding constant in biochemistry nomenclature. In the field of 

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