title: Reaction of human choriomammotropin with hydrogen peroxide.
abstract: Treatment of human choriomammotropin with hydrogen peroxide in the absence of denaturant was found to oxidize five of its six methionine residues to sulfoxide; the residue not oxidized was found to be methionine-170. This derivative was identical to the native hormone by exclusion chromatography, circular dichroism spectra, and rate of tryptic digestion, but suffered a very substantial drop in biological activity. In the presence of 8 M urea all of the methionines could be oxidized with hydrogen peroxide or alkylated with iodoacetic acid. The physical properties of these completely methionine-modified derivatives were significantly changed and biological activity had again been very substantially decreased. In control experiments, treatment of the native hormone with 8 M urea did not affect its physical, spectral or biological properties. Amino acid analysis of the derivatives was completely in accord with that expected.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D001681:Biological Assay; D002942:Circular Dichroism; D006801:Humans; D006861:Hydrogen Peroxide; D007700:Kinetics; D008715:Methionine / Q000032:analysis; D010446:Peptide Fragments / Q000032:analysis; D010928:Placental Lactogen; D011487:Protein Conformation
chemical_list: D000596:Amino Acids; D010446:Peptide Fragments; D010928:Placental Lactogen; D008715:Methionine; D006861:Hydrogen Peroxide