title: Oxidation reactions of a bovine serum albumin-bilirubin complex. A pulse radiolysis study.
abstract: Using the technique of pulse radiolysis, oxidation studies of the bovine serum albumin-bilirubin (BSA-BR) system with radicals like CCl3OO., N3., (SCN)2.-, Br2.- and OH. generated in neutral and alkaline medium are reported. In a neutral solution, BSA protects the bound BR very efficiently from the attack of these radicals. The experimental k/k' values for the reaction of CCl3OO., N3. and Br2.- radicals are 2.46, 1.78 and 2.55 respectively, where k and k' are the bimolecular rate constants for the formation of the semi-oxidized BSA and BR radicals respectively. The calculated ratios from our measurements of rate constants k and k' are 0.16, 0.28 and 1.38 for CCl3OO., N3. and Br2.- respectively. These values indicate protection of BR by BSA from free radical attack. For Br2.- radical-induced oxidation of the BSA-BR system, a radical transfer from protein to BR was observed. OH. shows very fast adduct formation with both BSA and BR. The bimolecular rate constant for the formation of BR-OH adducts at PH 8+/- 0.2 is 9.5 x 10(9) dm3 mol-1 s-1 (540 nm). OH. adds to BSA at neutral pH with a rate constant of 3.0 +/- 1.0 x 10(10) dm3 mol-1 s-1 (305 nm). In the BSA-BR complex, BSA fully protects BR from OH. attack and the (BSA-BR)-OH adduct further reacts with free BR molecule if present in solution.
authors.affiliation: Chemistry Division, Bhabha Atomic Research Centre, Bombay, India.
authors.forename: S
authors.initials: S
authors.lastname: Adhikari
authors.forename: C
authors.initials: C
authors.lastname: Gopinathan
mesh_terms: D000818:Animals; D001663:Bilirubin / Q000737:chemistry*; D001966:Bromine / Q000737:chemistry; D002417:Cattle; D005609:Free Radicals / Q000737:chemistry; D006133:Growth Substances / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry; D010084:Oxidation-Reduction; D011675:Pulse Radiolysis; D012709:Serum Albumin / Q000737:chemistry*; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D000075462:Serum Albumin, Human; D012996:Solutions; D013861:Thiocyanates / Q000737:chemistry; D014238:Trichloroacetic Acid / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D005609:Free Radicals; D006133:Growth Substances; D012709:Serum Albumin; D012996:Solutions; D013861:Thiocyanates; C053498:albumin-bilirubin complex; D014867:Water; D012710:Serum Albumin, Bovine; D017665:Hydroxyl Radical; D014238:Trichloroacetic Acid; D009584:Nitrogen; C031760:thiocyanate; D001663:Bilirubin; D001966:Bromine; D000075462:Serum Albumin, Human