OXIDATION OF RECOMBINANT HUMAN PARATHYROID-HORMONE - EFFECT OF OXIDIZED POSITION ON THE BIOLOGICAL-ACTIVITY

Purpose. To determine the oxidation products of recombinant human para thyroid hormone (rhPTH) treated with H2O2, the amino acid residue oxid ized, and the biological activity of the oxidation products. Methods. Oxidized residues were determined by CNBr cleavage, trypsin digestion. and subsequent fast atom bombardment mass spectrometry. The biologica l activity of each oxidized rhPTH was examined in rat osteosarcoma cel l adenylate cyclase assay. Results. Three oxidized products were isola ted, namely, Met at position 8 (Met8) sulfoxide, Met at position 18 (M etl8) sulfoxide and both positions Met sulfoxide. It appears that the Met8 and Metl8 oxidized forms are intermediates in the generation of t he Met doubly oxidized form. All oxidized forms possessed reduced biol ogical activity, more so for oxidation at Met8 than at Met18. Conclusi ons. The region around Met8 is important for the activity of the parat hyroid hormone.