Effect of Temperature on Catalytic Rates

The catalytic rate of conversion of the substrate-enzyme complex to product is controlled by k2 [see

Eq. (1)]. To eliminate the effect of factors listed in Section VII.A and B, the enzyme should be saturated with substrate and performed at the pH optimum for the enzyme-catalyzed reaction, over a temperature range where the enzyme is stable.

The rate constant, k2 = Vmax/[E]o, under the above conditions is plotted according to the Arrhenius equation:

where A is the Arrhenius constant, Ea is the Arrhenius activation energy, R is the universal gas constant (1.98 cal/mol deg), and T is degrees Kelvin. The plot is shown in Figure 16. From the right-hand slope, Ea is obtained. The positive slope (left side of Fig. 16) gives Ea for denaturation of the enzyme. The relationship between Ea and AH= from the Absolute Reaction Rate theory is given by Eq. (34).

The numerical difference between AH= and Ea is 0.6 kcal/mol at 25°C. a

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