Photo-isomerization and oxidation of bilirubin in mammals is dependent on albumin binding.
Anal Biochem
; 490: 34-45, 2015 Dec 01.
Article
in En
| MEDLINE
| ID: mdl-26297581
ABSTRACT
The bilirubin (BR) photo-conversion in the human body is a protein-dependent process; an effective photo-isomerization of the potentially neurotoxic Z,Z-BR as well as its oxidation to biliverdin in the antioxidant redox cycle is possible only when BR is bound on serum albumin. We present a novel analytical concept in the study of linear tetrapyrroles metabolic processes based on an in-depth mapping of binding sites in the structure of human serum albumin (HSA). A combination of fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular modeling methods was used for recognition of the binding site for BR, its derivatives (mesobilirubin and bilirubin ditaurate), and the products of the photo-isomerization and oxidation (lumirubin, biliverdin, and xanthobilirubic acid) on HSA. The CD spectra and fluorescent quenching of the Trp-HSA were used to calculate the binding constants. The results of the CD displacement experiments performed with hemin were interpreted together with the findings of molecular docking performed on the pigment-HSA complexes. We estimated that Z,Z-BR and its metabolic products bind on two independent binding sites. Our findings support the existence of a reversible antioxidant redox cycle for BR and explain an additional pathway of the photo-isomerization process (increase of HSA binding capacity; the excess free [unbound] BR can be converted and also bound to HSA).
Key words
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Bilirubin
/
Serum Albumin
/
Models, Molecular
/
Photochemical Processes
Type of study:
Prognostic_studies
Limits:
Animals
/
Humans
Language:
En
Journal:
Anal Biochem
Year:
2015
Type:
Article