The deconvolution of multi-state transition DSC curves of biological macromolecules: bovine serum albumin and bovine seminal ribonuclease.

The denaturation of the ordered, specific structures of biological macromolecules is a highly cooperative process which many researchers have likened to the melting or solution of a crystal. However, with increasing numbers of studied systems using different experimental approaches, it has become clear that only some small globular proteins undergo a two-state transition. Differential scanning microcalorimetry, giving direct thermodynamic information, has proved to be very useful in clarifying the details of the unfolding processes. For the same reasons, it can provide a reliable experimental basis for developing more complex models. In this paper, two proteins are considered: bovine seminal ribonuclease, which consists of two identical sub-units, covalently bonded; and bovine serum albumin, a protein formed by three domains, two of which are probably strongly interacting. Two possible kinds of mechanisms have been tested: the independent transition process and the sequential denaturation. Both approaches give satisfactory results and the apparent contradiction is discussed on the basis of the particularly compact structure of these macromolecules.