The Causes of Sharply Bent or Discontinuous Arrhenius Plots for Enzyme‐Catalysed Reactions

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Abstract
Two models are proposed to account for the abrupt changes in the enthalpy of activation (ΔH*) that are sometimes observed, without corresponding abrupt changes in the maximum velocity (V), at apparent transition temperatures in the Arrhenius plots of enzyme‐catalyzed reactions. Both models predict that a small but observable discontinuity in V will usually occur, which distinguishes such plots from the sharply bent but continuous plots that result when the individual rate constants contributing to V have widely different temperature dependencies. One model applies to membrane‐bound enzymes only, and predicts that ΔH* will always be smaller above the transition. The other applies to both soluble and membrane‐bound enzymes, and can account for either an increase or a decrease in ΔH* as the temperature is raised.