The kinetics of soil acid phosphatase

The kinetics of enzyme systems in soil can reasonably be expected to be similar to those of immobilised enzymes and therefore be modified by factors not considered in the formulation of the classical Michaelis-Menten model of enzyme kinetics. Previous studies of the p-nitrophenyl phosphatase activity of soil have assumed that the system follows Michaelis-Menten kinetics. This paper reports experiments on the p-nitrophenyl phosphatase activity of a kraznozem in which the plotting of V₀, the initial rate. against $\text{V}{}_0\text{[S]}\text{where}$ [S] is the substrate concentration showed that the system, for this soil at least, does not follow Michaelis-Menten kinetics. An evaluation of the graphical techniques used in previous studies showed that the conclusion that the p-nitrophenyl phosphatase activity of soil follows Michaelis-Menten kinetics is based on doubtful premises. Experiments in which both the substrate and the product were measured spectrophotometrically at intervals throughout the hydrolysis of p-nitrophenyl phosphate by the kraznozem yielded evidence for a model of the system which is capable of accounting for the deviation from Michaelis-Menten kinetics.