The existence of es complexes has been shown in a variety of ways At a constant concentration of enzyme, the reaction rate increases with increasing substrate concentration until a maximal velocity is reached (Figure 8-8). In contrast, uncatalyzed reactions do not show this saturation effect. In 1913. Leonor Michaelis interpreted the maximal veloc ity of an enzyme-calalyzed reaction in terms of the formation of a discrete Es complex. At a sufficiently high substrate concentration, the catalytic sites are filled and so the reaction rate reaches a maximum. Though indirect this is the most general evidence for the existence of ES complexes