Kinetics of thermal denaturation of met‐hemoglobin in perturbed solvent: Relevance of bulk‐electrostatic and hydrophobic interactions

We studied the kinetics of the heat denaturation (at 50°C) of met‐hemoglobin in the presence of various monohydric alcohols. The denaturation rate was slowed by the presence of small concentrations of methanol and ethanol; in all the other cases, i.e., at high concentrations of methanol and ethanol, and in the whole concentration range studied for iso‐ and n‐propanol, an increase in the denaturation rate was observed. Following a procedure already applied to the study of the effects of the same alcohols on the reaction of hemoglobin with oxygen, we separated the overall observed effects into contributions related to the variation of the bulk dielectric constant of the medium (bulk‐electrostatic contributions) and contributions not related to variations in this parameter (nonbulk‐electrostatic contributions). For all the alcohols, we found a unique correlation law connecting the above nonbulk‐electrostatic contributions with the analogous ones previously reported for the T → R transition of hemoglobin. This fact strongly supports the validity of the procedure used and suggests that nonbulk‐electrostatic contributions, relative to these two different processes, have a common background and are univocally determined by the extent of the “solvent perturbation” imposed by the presence of the perturbing cosolvents.