Equilibrium Constant and the Haldane Relationship

At equilibrium, both reversible reactions (3.20) and (3.31) come to a dynamic standstill, although the reaction has not stopped. An equihbrium constant for the overall process AP, for reaction (3.20), is equal to 

Using Eqs. (3.38) and (3.39), one can cast the general reversible forms of the Michaelis-Menten equations ((3.24) and (3.36)) into another useful form  

Equation (3.40) is quite general and describes the effect of reactant concentration on rate, not only at the start of the reaction in the complete absence of P (in the forward direction) or A (in the reverse direction), but also at any time during the approach to equilibrium (Alberty, 1959 Qeland, 1963, 1977). 

Equation (3.41) is known as the Haldane relationship (Haldane, 1930). It is a very important relationship, because it states that the luetic parameters of every reversible enzymatic reaction are not independent of one another and are limited by the thermodynamic equihbrium constant of the overall reaction. 

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