TYROSINE - AN INHIBITOR OF LDL OXIDATION AND ENDOTHELIAL-CELL CYTOTOXICITY INITIATED BY SUPEROXIDE NITRIC-OXIDE RADICALS

Tyrosyl radicals can catalyze LDL oxidation. In addition to their LDL oxidizing ability, superoxide (O2(.-))/nitric oxide (NO.) generate phe noxyl radicals when reacting with tyrosine. Therefore we tested if tyr osine can act as a pro-oxidant in O-2(.-)/NO.-initiated LDL oxidation. When LDL was exposed to O-2(.-)/NO., tyrosine exerted a strong inhibi tory effect on O-2(.-)/NO.-initiated LDL oxidation as measured by TBAR S formation and alteration in electrophoretic mobility of LDL. Tyrosin e was also able to protect human endothelial cells from the cytotoxic effect of O-2(.-)/NO.. Because O-2(.-)/NO. can occur in vivo, the resu lts may indicate that serum-free tyrosine could act as an efficacious physiological antioxidant in case of O-2(.-)/NO.-initiated LDL oxidati on and endothelial cell cytotoxicity. (C) 1997 Federation of European Biochemical Societies.