The Michaelis-Menten model of the variation of the rate of an enzyme-catalysed reaction with concentration of the substrate is given by

Where S is the substrate concentration (mmol L^-1), v_max is the maximum velocity (mmol s^-1), and K_M is the Michaelis constant (mmol L^-1).

Notice that when S << K_M, the rate is proportional to S; when S >> K_M, the rate is independent of S.

To graph the variation of the reaction rate enter the parameters (i.e., v_max, K_M) and hit New Plot. Up to 5 plots can be displayed at one time. The Clear button will remove all plots. To see the parameters for each plot hit the Legend on/off button. The Redraw button will refresh the graph. This is useful when the function domain (i.e., S ) has been changed. To see the value of each plot at a given point, move your cursor to the desired location then click and hold.