Conformation inversion of bilirubin formed by reduction of the biliverdin-human serum albumin complex: evidence from circular dichroism.
As shown by circular dichroism spectroscopy, biliverdin preferentially adopts an M-helicity conformation on human serum albumin in aqueous buffer, pH 7.5, whereas biliverdin exhibits only a weak preference for the P-helicity conformation on bovine serum albumin at the same pH. Upon rapid reduction of the complexes with sodium borohydride, P-helicity bilirubin-IX alpha is obtained on the human albumin complex, and M-helicity bilirubin-IX alpha is obtained on the bovine serum albumin complex. Thus, biliverdin in effect undergoes an inversion of chirality upon reduction. Since the reduction did not afford a rubin with the same helicity as that of the verdin, the observations point to a hitherto undetected conformational mobility of albumin-bound bilirubin.
Trull
F R
FR
Departament de Química Orgànica, Universitat de Barcelona, Catalunya, Spain.
Ibars
O
O
Lightner
D A
DA
D001663:Bilirubin / Q000737:chemistry* / Q000378:metabolism*; D001664:Biliverdine / Q000737:chemistry* / Q000378:metabolism*; D002942:Circular Dichroism; D006801:Humans; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D012709:Serum Albumin / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000378:metabolism
D012709:Serum Albumin; D012710:Serum Albumin, Bovine; D001664:Biliverdine; D001663:Bilirubin