SPECIES-DIFFERENCES OF SERUM ALBUMINS - III - ANALYSIS OF STRUCTURAL CHARACTERISTICS AND LIGAND-BINDING PROPERTIES DURING N-B TRANSITIONS

Purpose. The aim of this study was to investigate the characteristics of the structural transitions and changes in ligand binding properties of different albumins during the pH-dependent structural transition, often referred to as the N-B transition. Methods, Structural transitio ns were evaluated by means of spectrometry, differential scanning calo rimetry and chemical modification. In addition, ligand binding propert ies were investigated using typical site-specific bound drugs (warfari n, phenylbutazone, ibuprofen and diazepam). Results. Conformational ch anges, including N-B transition, clearly occurred in albumins from all species used in this study. The conformational stabilities of all the albumins were clearly lost in the weakly alkaline pH range. This was probably the result of the destruction of salt bridges between domain I and domain III in the albumin molecule. In addition, the profiles of the ANS-induced fluorescence were different and could be classified i nto two patterns, suggesting that hydrophobic pockets in the albumin m olecules were different for the different species. The data suggest th at the amino acid residues responsible for the transitions were some o f the His residues located in domain I. Further, the ligand binding pr operties of the albumins were slightly different but statistically sig nificant. Conclusions. The overall mechanisms of the N-B transition ma y be similar for all the albumins, but its impact is considerably diff erent among the species in terms of both structural characteristics an d ligand binding properties. Furthermore, the transitions appear to be multistep transitions.