Temperature Behaviour of Human Serum Albumin

Abstract

Structural alterations of albumin, their dependence on concentration and the role of free -SH groups at thermal denaturation, as well as the reversibility of thermally induced structural changes, were studied. Application of various physical methods provides information on a series of structural parameters in a major concentration range. Apart from changes of the helix content, heat treatment gives rise to β structures which are amplified on cooling and which are correlated with the aggregation of albumin. With rising temperature and concentration the proportion of β structures and aggregates increases. At degrees of denaturation of up to 20% complete renaturation is possible in every case. The structure content is concentration-dependent even at room temperature. It may be that intermolecular interactions induce additional α-helix structures which are less stable, however, than the ones stabilized by intramolecular interactions. Unfolding of the pocket containing the free -SH group of cysteine-34 enables disulphide bridges to be formed leading to stable aggregates and irreversible structural alterations. Through binding of N-ethylmaleimide to free -SH groups, which blocks the formation of disulphide bridges, it is possible to prevent aggregation and irreversible conformational changes. At temperatures below 65–70°C, oligomers are formed mainly via intermolecular β structures.