Vmax

 V_max is the notation used to describe the maximum velocity at which a reaction can occur. Once V_max is reached a reaction cannot proceed any faster, regardless of how much extra substrate is added.  The relationship between the enzymes rate of reaction and the substrate is defined as the K_m (Michaelas Constant) of the enzyme. There relationship is defined by the following equation:   v = V_max / (1 + (K_m/[S]))