BILIRUBIN AS AN ANTI PRECIPITANT AGAINST COPPER MEDIATED DENATURATIONOF BOVINE SERUM-ALBUMIN - FORMATION OF COPPER-BILIRUBIN COMPLEX

BR forms a beautiful 1 : 1 greenish complex with Cu2+, having a charac teristic absorption maximum at 343 nm. To our knowledge, this is the f irst metal complex of bilirubin in aqueous solution so far to be repor ted. It has also been shown that bilirubin (BR) at a concentration mor e than protein binding capacity has a definite role as an anti precipi tant of bovine serum albumin by excess copper. At a concentration of 1 X 10(-3) moll(-1) of the Cu-BR complex, the colour becomes greenish b lack. The rate of formation of this Cu-BR complex when BR extracts cop per from copper-albumin complex as obtained in our experiment is 34.98 1mol(-1) s(-1). The Cu-BR complex is stable at a pH ranging from 3.5 t o 13.2. and also can scavenge radicals like CCl3OO., e(aq)(-) and OH.. Addition of excess copper sulfate to the solution of this complex cau ses a greenish black precipitate which can be re dissolved in HCl but insoluble in 99% ethanol. The complex does not give positive test in G melin reaction for bile pigments. The fluorescence spectrum of the com plex in solution exhibits a peak at 450 nm when excited at 343 nm. The precipitated complex is insoluble in a number of solvents like ether, xylene, benzene, acetone, chloroform-methanol mixture and DMSO. These results show that BR may protect mammals from copper poisoning. (C) 1 998 Elsevier Science B.V.