DSC study of the postdenaturated structures in biopolymer-water systems

The temperature dependences of heat capacity for water-denaturated biopolymer (globular proteins, collagen and DNA) were measured in a wide range of temperatures (0-140 degreesC) and water content of the systems. It has been shown that thermally denaturated globular proteins (lysozyme, myoglobin and catalase) are able to form the thermoreversible heat-set structures under the certain conditions studied. The additional endothermal maximum observed is the calorimetric manifestation of the phase transition related to the melting of these thermotropic non-native structures. The melting gels are completely formed just after denaturation during relatively short time and only their prolonged state at T >T-d leads to their transformation to thermoirreversible non-melting ones. The postdenaturated structures from water-denaturated protein (Mb, Lys and RN-ase) systems with a different amount of free water were also studied. The thermoreversible cold-set gels are formed from both water-denaturated DNA and water-denaturated collagen systems. These thermotropic structures are metastable. A spatial gel network of both collagen and DNA is formed from the native-like renaturated structures.