Temperature dependence of reactions and activation parameters

In the last section it was stated that most biologists wisely restrict themselves to the pragmatic approach of just finding the temperature dependence of a process as useful information . However, it is necessary for us to give some attention to the interpretation of Arrhenius plots and its pitfalls. Besides the purely descriptive how much faster is the reaction when the temperature is raised by ten degrees (see the previous section), there are questions which can be answered relating to reaction mechanisms, to the 

In subsequent sections we shall find that the heat of activation, derived from Arrhenius plots, gives pointers to the character of the reaction. For instance, reactions which are controlled by the rate of diffusion have very low energy barriers (30 to 40 kJ mole ), as have the elastic processes in muscle fibres (see Davis Harrington, 1993), while reactions involving protein conformation changes characteristically have values three to four times as large. The major difficulties in the interpretation of many reports 

If a reaction depends on the state of ionization of a reactant then the temperature dependence of the process will have, as one of its components, the effect of temperature on the ionization equilibrium. Analogous to the rapid pre-equilibrium mechanism of ligand binding (see section 3.2) in the reaction 

Another feature of the analysis of the temperature dependence of reaction velocities, which has received much attention and frequently dubious interpretation, is the non-linearity of the Arrhenius plot. Moore Pearson (1981) use the term anti Arrhenius plots for some of their graphical representations of rates which first increase and then decrease as the temperature is raised. They state, correctly, that such graphs usually result from multi-step mechanisms or a change in mechanism as the temperature increases. 

One has to distinguish between results indicating a decrease in rate as temperature is increased and the conclusion that the rate would increase as the temperature is decreased. Tests of reversibility of the effect of any change in condition on the rates of reactions are of particular importance in 

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