The influence of temperature on the binding of AMP to phosphorylase b

Equilibrium dialysis measurements have been performed at several temperatures, ranging from 5 to 30°C, to calculate the binding constants of AMP to phosphorylase b (EC 2.4.1.1). ΔH = ?10 kcal/mol and ΔS = ?6.4 e.u. have been obtained for the binding process. Measurements of enzymatic activity have been performed in the same temperature range. An activation energy of 16 kcal has been calculated for the enzyme-catalysed reaction. Absorption difference spectra induced by AMP in phosphorylace b when AMP is bound to its high affinity site have also been carried out at these temperatures. The equilibrium constant for the binding of AMP to phosphorylase b, the enzyme activity as well as the molar absorption coefficient of the absorption difference spectra studied show no discontinuity with temperature from 5 to 30°C.