Hydroxopentaamminechromium(III) promoted phosphorylation of bovine serum albumin: its potential implications in understanding biotoxicity of chromium

Evidence for chromium(III) induced phosphorylation of a biomarker protein b ovine serum albumin (BSA) is presented. Radiolabelled adenosine 5'-triphosp hate (ATP) was reacted with BSA in the presence of various Cr(III) salts. W hile [Cr(NH3)(5)(H2O)](3+) brought about phosphorylation of BSA, several Cr (III) complexes, viz. [Cr(bpy)(3)](3+), [Cr(phen)(3)](3+), [Cr(en)(3)](3+), [Cr(salen)(H2O)(2)](+) and [Cr(salprn)(H2O)(2)](+), did not phosphorylate BSA. The Cr(III) mediated the transfer of gamma- and a-phosphates but not t he adenine and the sugar moieties of the ATP molecule to BSA. The observed stoichiometry was 0.75 mol P-i to mol BSA for the gamma-phosphate and 0.5 m ol P-i to mol BSA for the alpha-phosphate of ATP. The presence of serine ph osphate and threonine phosphate was detected in the hydrolysate of phosphor ylated BSA by means of comparison of R-f values with authentic samples of p hosphoserine and phosphothreonine after chromatographic separation and auto radiography. [Cr(NH3)(5)(H2O)](3+) at pH 7.4 is known to exist as the conju gate base [Cr(NH3)(5)(OH)](2+) and is capable of ligand substitution involv ing metal-oxygen bond retention. Such anation reaction of [Cr(NH3)(5)(OH)]( 2+) with ATP subsequently leads to the esterification of alcoholic hydroxyl groups of serine and threonine of BSA. Possible consequences of chromium(I II) induced in vivo phosphorylation of proteins are discussed. (C) 1999 Els evier Science B.V. All rights reserved.