Most of the enzyme catalyzed biological reactions are reversible in nature. However, an enzyme may prefer to catalyze the reaction more efficiently in one direction over the other under given physiological concentrations of substrate or product (substrate in the reverse direction). An enzyme favouring a virtual unidirectional catalysis of an overall reversible reaction can’t escape the laws of thermodynamics. As a catalyst doesn’t change the equilibrium constant of a reaction but only modifies the approach towards equilibrium, in order to enhance reaction velocity, in same way, even a so-called ‘one way enzyme’ is constrained to maintain the same equilibrium constant in either direction. Haldane has successfully put together kinetic parameters (dependent on enzyme properties) and equilibrium constant (independent of enzyme properties) into what is known as the ‘Haldane relationship’, which helps conclude the ‘correctness’ of a plausible enzyme reaction mechanism.
J.B.S. Haldane; equally known for his contributions in physiology and genetics, gave ‘Haldane relationship’ in 1930s:
Consider a Uni-Uni reaction: S↔P
Michaelis Menten equation for the reversible reaction is as follows: …show more content…
The challenge however is to interpret the constants defined for a reaction as a whole in terms of those for individual steps. In this regard, using the Haldane relationship, one can determine kinetic constants in terms of the equilibrium constant and also check if the proposed reaction mechanism is thermodynamically allowed. The kinetic constants so calculated are generally limited by precision unlike the equilibrium