title: Binding to Bovine Serum Albumin Protects β-Carotene against Oxidative Degradation.
abstract: Binding to bovine serum albumin (BSA) was found to protect β-carotene (β-Car) dissolved in air-saturated phosphate buffer solution/tetrahydrofuran (9:1, v/v) efficiently against photobleaching resulting from laser flash excitation at 532 nm. From dependence of the relative photobleaching yield upon the BSA concentration, an association constant of Ka = 4.67 × 10(5) L mol(-1) for β-Car binding to BSA was determined at 25 °C. Transient absorption spectroscopy confirmed less bleaching of β-Car on the microsecond time scale in the presence of BSA, while kinetics of triplet-state β-Car was unaffected by the presence of oxygen. The protection of β-Car against this type of reaction seems accordingly to depend upon dissipation of excitation energy from an excited state into the protein matrix. Static quenching of BSA fluorescence by β-Car had a Stern-Volmer constant of Ksv = 2.67 × 10(4) L mol(-1), with ΔH = 17 kJ mol(-1) and ΔS = 142 J mol(-1) K(-1) at 25 °C. Quenching of tryptophan (Trp) fluorescence by β-Car suggests involvement of Trp in binding of β-Car to BSA through hydrophobic interaction, while the lower value for the Stern-Volmer constant Ksv compared to the binding constant, Ka, may indicate involvement of β-Car aggregates. Bound β-Car increased the random coil fraction of BSA at the expense of α-helix, as shown by circular dichroism, affecting the β-Car configuration, as shown by Raman spectroscopy.
authors.affiliation: Department of Chemistry, Renmin University of China , Beijing 100872, People's Republic of China.
authors.forename: Hui-Ting
authors.initials: HT
authors.lastname: Chang
authors.affiliation: Department of Chemistry, Renmin University of China , Beijing 100872, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Cheng
authors.affiliation: Department of Chemistry, Renmin University of China , Beijing 100872, People's Republic of China.
authors.forename: Rui-Min
authors.initials: RM
authors.lastname: Han
authors.affiliation: Department of Chemistry, Renmin University of China , Beijing 100872, People's Republic of China.
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Zhang
authors.affiliation: Food Chemistry, Department of Food Science, University of Copenhagen , Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D005453:Fluorescence; D007700:Kinetics; D010084:Oxidation-Reduction; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D019207:beta Carotene / Q000737:chemistry*
chemical_list: D019207:beta Carotene; D012710:Serum Albumin, Bovine
keywords: bovine serum albumin; photodegradation; protein binding; β-carotene