Thermochemistry of the Avidin‐Biotin Reaction

The enthalpy for the binding of biotin to avidin has been determined at 25, 34 and 43°C (pH 9, ammonium acetate buffer): ΔH(25°C) =–22.5 ± 0.1 kcal/mol biotin; ΔCp=–237 ± 12 cal × mol biotin−1× K−1.Solubilities and enthalpies of solution of biotin in water and in ethanol were determined at 25°C. The transfer process for biotin between water and ethanol was considered as a simple model for the protein binding process.