Conformational changes in the bilirubin-human serum albumin complex at extreme alkaline pH.
Light-absorption, c.d. and fluorescence of the bilirubin-albumin complex were investigated at extreme alkaline pH. Above pH 11.1 albumin binds the bilirubin molecule, twisted oppositely to the configuration at more neutral pH. On the basis of light-absorption it is shown that two alkaline transitions occur. The first alkaline transition takes place at pH between 11.3 and 11.8, co-operatively dissociating at least six protons. The second alkaline transition takes place at pH between 11.8 and 12.0. It probably implies a reversible unfolding of the albumin molecule, increasing the distance between tryptophan-214 and bilirubin, and partly exposing the liganded bilirubin to the solvent.
D001663:Bilirubin / Q000378:metabolism*; D002942:Circular Dichroism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D046911:Macromolecular Substances; D011487:Protein Conformation; D011522:Protons; D012709:Serum Albumin / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry
D046911:Macromolecular Substances; D011522:Protons; D012709:Serum Albumin; D001663:Bilirubin