Thermal Denaturation of Collagen Analyzed by Isoconversional Method Sergey Vyazovkin, * Luc Vincent,Nicolas Sbirrazzuoli Introduction The fibrous protein collagen is the major biopolymer pre- sent in animal connective tissue. In its native folded form, collagen has a triple helical structure,whose individual strands are held together by hydrogen bonds. Heating of collagen results in its thermal denaturation, during which the hydrogen bonds break, and the helices unfold, forming coils.Because of appreciable heat absorption, the process can be monitored by calorimetry.The kinetics of the thermal denaturation of collagen is of a significant interest from the standpoint of practical applications such as laser surgery, thermal therapy, tissue engineering. Unfolding of proteins is a complex phenomenon that involves interplay of kinetic and thermodynamic factors. A simplified scheme of the process was proposed by Lumry and Eyring [1] N , K U ! k D (1) where K is the equilibrium constant of the reversible step and k is the rate constant of the irreversible step, and N,U, and D stand respectively for the native, unfolded,and de- natured forms. The model appears mostly suitable for dena- turation occurring under conditions of high irreversibility. [2] The kinetics of the thermal denaturation of proteins is most widely treated as a single first-order irreversible step N ! D, [3,4] whose rate dependence on temperature obeys the Arrhenius equation, k ¼ Aexp E RT (2) where E is the activation energy, A is the pre-exponential factor,R is the gas constant, and T is the absolute tempe- rature. Such approach yields a single value of the effective Communication An isoconversional method is proposed to be used for evaluating activation energy of protein denaturation. Applied to DSC data on collagen denaturation, the method yields an activation energy that decreases throughout the process. The Lumry-Eyring model gives an explanation for this decrease and affords estimates for the enthalpy of the reversible step and the activation energy of the irreversible step of denaturation. The reversible unfolding is detectable by multi-frequency temperature-modulated DSC. S. Vyazovkin Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294, USA Fax: (205) 975 0070; E-mail: vyazovkin@uab.edu L.Vincent,N. Sbirrazzuoli Thermokinetic Group, Laboratory of Chemistry of Organic and Metallic Materials, Institute of Chemistry of Nice, University of Nice - Sophia Antipolis, 06108 Nice Cedex 2, France Macromol.Biosci.2007,7, 1181–1186 ß 2007 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim DOI: 10.1002/mabi.2007001621181