The "k obs " method in reversible enzyme inhibition kinetics consists of analyzing the reaction time-course in two consecutive steps. In the first phase of the data analysis, each individual kinetic trace is analyzed separately to determine an apparent first-order rate constant using an appropriate algebraic model for the reaction progress. In the second step, the values of apparent first-order rate constants so determined are fit to another algebraic model, which is based on a presumed mechanism of inhibition. For example, depending on the exact nature of the mathematical relationship between k obs and the inhibitor concentration [I] 0 , it might be possible to determine whether or not the enzyme-inhibitor interaction proceeds with an involvement of a transient intermediate.