Vmax

In accordance with the Michaelis-Menten equation, the initial reaction rate (V₀) increases at increased substrate concentrations ([S]). The reaction rate increases more at lower substrate concentrations, and it eventually reaches a plateau, approaching the maximum velocity (V_max) (Fig. 1). The maximum initial velocity is reached when the enzyme is saturated, when enough substrate is present to ensure that practically all the enzyme is part of the enzyme-substrate complex. Because the enzyme can never be completely saturated, V_max is never fully reached. V_max is dependent on 2 things: the turnover number of the enzyme (k_cat), and the concentration of the enzyme ([E]) [1].

Vmax = [E] • kcat

Thus, a higher [E] leads to a higher V_max. The turnover number will be described in more detail on the following page.

Figure 1: An illustration of the Lineweaver-Burk equation fitted to a double-reciprocal transformation of an enzyme kinetic dataset.

Determining V_max

Just like k_m, V_max can be determined using the Lineweaver-Burk equation (Figure 1):

1/V₀ = 1/V_max + K_m/V_max • 1/[S]

Based on this equation, a straight line fitted to a double reciprocal plot will have the y-intercept 1/V_max, and V_max can therefore be obtained by taking the reciprocal to this intercept [1].

References

1. Lehninger, Albert L.; Nelson, David L.; Cox, Michael M. (2008). Principles of Biochemistry (5th ed.). New York, NY: W.H. Freeman and Company. ISBN 978-0-7167-7108-1.

K_m

k_cat

Theory overview