RESUMO
Reports on nonenzymatic oxidation of human growth hormone (hGH) have been previously limited to methionyl residues (Met14 and Met125). We report on the oxidation of a histidyl residue in hGH treated with intense light. The photooxidation process is predominately site-specific to histidine at position 21, which forms a cation-binding site along with His18 and Glu174. This site binds metal ions and, under intense light, catalyzes the oxidation of His21. Products are formed by the addition of one, two, or three atoms of oxygen to the histidyl residue.
Assuntos
Histidina/metabolismo , Hormônio do Crescimento Humano/metabolismo , Fotoquímica , Sítios de Ligação , Cromatografia Líquida de Alta Pressão , Cromatografia por Troca Iônica , Humanos , Modelos Moleculares , Oxirredução , Oxigênio/metabolismo , Mapeamento de Peptídeos , Zinco/metabolismoRESUMO
Highly purified human relaxin, produced by combining chemically synthesized A- and B-chains, was analyzed by reversed-phase high-performance liquid chromatography, ion-exchange chromatography and tryptic mapping in order to ascertain purity of the material, presence of uncleaved protecting groups, correctness of disulfide linkages and presence of deamidated or oxidized variants. It was shown by a variety of analytical methods that the product was of high purity; a minimum purity level as judged by the most discriminating assay was greater than 98%. Components of the relaxin preparation removed during the purification were identified to be variants containing deletions arising from incomplete coupling reactions in the solid phase peptide synthesis and/or oxidized methionine residues.
