Analysis of Metabolic Control:- The Elasticity Coefficient Is Related to an Enzyme’s Responsiveness to Changes in Metabolite or Regulator Concentrations
A second parameter, the elasticity coefficient, ɛ, ex presses quantitatively the responsiveness of a single en zyme to changes in the concentration of a metabolite or regulator; it is a function of the enzyme’s intrinsic kinetic properties. For example, an enzyme with typical Michaelis-Menten kinetics shows a hyperbolic response to increasing substrate concentration (Fig. 15–35). At low concentrations of substrate (say, 0.1 Km) each increment in substrate concentration results in a comparable increase in enzymatic activity, yielding an near 1.0. At relatively high substrate concentrations (say, 10 Km), increasing the substrate concentration has little effect on the reaction rate, because the enzyme is already saturated with substrate. The elasticity in this case ap proaches zero. For allosteric enzymes that show positive cooperativity, ɛ may exceed 1.0, but it cannot exceed the Hill coefficient. Recall that the Hill coefficient is a measure of the degree of cooperativity, typically between 1.0 and 4.0.
FIGURE 15–35 Elasticity coefficient, ɛ, of an enzyme with typical Michaelis-Menten kinetics. At substrate concentrations far below the Km, each increase in [S] produces a correspondingly large increase in the reaction velocity, v. For this region of the curve, the enzyme has an elasticity, ɛ, of about 1.0. At [S]>> Km, increasing [S] has little effect on v; ɛ here is close to 0.0
