In 1925, George Edward Briggs and George Burdon Sanderson Haldane derived a new interpretation of the enzyme kinetics law described by Victor Henri in 1903, different from the 1913 Michaelis–Menten equation. Leonor Michaelis and Maud Menten assumed that enzyme (catalyst) and substrate (reactant) are in fast equilibrium with their complex, which then dissociates to yield product and free enzyme. The Briggs–Haldane equation was of the same algebraic form, but their derivation is based on the quasi steady state approximation, that is the concentration of intermediate complex (or complexes) does not change. As a result, the microscopic meaning of the "Michaelis Constant" (km) is different. Although commonly referring it as Michaelis–Menten kinetics, most of the current models actually use the Briggs–Haldane derivation.

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