Figure 1. Enzymes accelerate the rates of chemical reactions by stabilizing (lowering the potential energy of) the transition state of the reaction. The enzyme (E) and substrate (S) first combine to form the ES complex. The bound substrate is then converted to the bound transition state (ES*), which is energetically stabilized relative to the free transition-state molecule (S*). The enzyme-bound transition state is then converted to enzyme-bound product (EP), and finally the product (P) is released. Adapted from Copeland RA (2000) Enzymes: A Practical Introduction to Structure, Mechanism and Data Analysis, 2nd edn. New York: Wiley, with permission of the author.

Figure 2. Graphical determination of the kinetic constants K_m and k_cat. The production of product over time in an enzyme-catalysed reaction proceeds with pseudo-first-order kinetics (a), slowing down as substrate supplies are diminished. The shaded area in (a) is shown on an expanded scale in (b). Here, the product increases linearly with time in the early phase of the reaction, and the initial velocity can therefore be estimated by the slope of the linear fit. The initial velocity thus measured increases with increasing initial concentration of substrate [S] over a finite range (c). A replot of the initial velocity as a function of substrate concentration (d) allows determination of the values of K_m and V_max by fitting to eqn ( [link to mathDisplay id="a0002702-mdis-0001" numbered="no", but no linkLabel in the xref] ). The value of k_cat is then determined by dividing V_max by the enzyme concentration [E].