An analysis of the kinetics of enzymatic systems with unstable species

We present a general kinetic analysis of the Michaelis-Menten mechanism for the case in which the substrate, the enzyme-substrate complex, and the product are unstable. The equations for the rapid equilibrium conditions are obtained as a particular case of the general equations of the transient-phase. The kinetic data analysis which we suggest is based on the time progress curve of the product of the enzymatic reaction, or on the progress curve of the species into which the immediate product is transformed. This analysis allows the determination of the rate and equilibrium constants if adequate experimental results are available. It assumes, in contrast to most previous treatments of enzyme kinetics, that the concentration of the enzyme is much higher than that of the substrate. Since this condition often is satisfied inside cells, it can be more relevant to physiological problems than the classical assumption, [E] << [S], which sooner pertains to the situation in the laboratory.