Analysis of binding interaction between the natural apocarotenoid bixin and human serum albumin by circular dichroism and fluorescence spectroscopy.

TitleAnalysis of binding interaction between the natural apocarotenoid bixin and human serum albumin by circular dichroism and fluorescence spectroscopy.
Publication TypeJournal Article
Year of Publication2005
AuthorsZsila, F, Molnár, P, Deli, J
JournalChem Biodivers
Volume2
Issue6
Pagination758-72
Date Published2005 Jun
ISSN1612-1880
KeywordsBinding Sites, Carotenoids, Circular Dichroism, Humans, Models, Molecular, Molecular Structure, Protein Binding, Protein Conformation, Serum Albumin, Spectrometry, Fluorescence
Abstract

Bixin is an important, pharmacologically active dietary cis-carotenoid, but its interaction with potential macromolecular targets is completely unexplored. This work was aimed to study the binding of bixin to human serum albumin (HSA), the most abundant protein in blood plasma. Circular dichroism (CD) spectroscopy in combination with UV/VIS absorption spectroscopy and fluorescence quenching techniques were applied. Appearance of induced CD bands in the UV- and VIS-absorption spectral regions indicated the formation of non-covalent carotenoid-albumin complexes. Shape and spectral position of the extrinsic Cotton effects suggested the binding of a single bixin molecule to HSA in chiral conformation. Scatchard and non-linear regression analyses of CD titration data resulted in similar values for the association constant (Ka = 6.6 and 4.6x10(5) M(-1), resp.) and for the number of binding sites (n = 1). The binding interaction was independently confirmed by fluorescence-quenching experiment from which the binding parameters were also calculated. CD Displacement measurements performed with marker ligands established that the main drug binding sites of HSA are not involved in binding of bixin. Palmitic acid decreased the amplitude of the induced CD bands suggesting a common albumin binding site for bixin and long-chain fatty acids. The above data indicate that HSA plays a significant role in the plasma transportation of bixin and related dietary carboxylic acid carotenoids.

DOI10.1002/cbdv.200590053
Alternate JournalChem. Biodivers.
PubMed ID17192019