Analysis of differential scanning calorimetry data for proteins. Criteria of validity of one-step mechanism of irreversible protein denaturation.

We consider in this work the analysis of the excess heat capacity C(p)(ex) versus temperature profiles in terms of a model of thermal protein denaturation involving one irreversible step. It is shown that the dependences of ln C(p)(ex) on 1 T (T is the absolute temperature) obtained at various temperature scanning rates have the same form. Several new methods for estimation of parameters of the Arrhenius equation are explored. These new methods are based on the fitting of theoretical equations to the experimental heat capacity data, as well as on the analysis of the dependence d(ln C (p)(ex)) d ( 1 T ) on 1 T . We have applied the proposed methods to calorimetric data corresponding to the irreversible thermal denaturation of Torpedo californica acetylcholinesterase, cellulase from Streptomyces halstedii JM8, and lentil lectin. Criteria of validity for the one-step irreversible denaturation model are discussed.