title: Serine-578 is a major phosphorylation locus in human plasma plasminogen.
abstract: It has been reported that human plasminogen (HPg) exists in plasma in a phosphorylated form. We now document that both major glycoforms of plasma HPg contain a phosphoserine residue in their latent protease chains, as revealed by quantitative protein phosphate determinations and 31P-NMR analysis. The sequence location of the phosphoserine residue was established by time-of-flight matrix-assisted laser desorption ionization with delayed extraction mass spectrometric analysis of peptides resulting from complete tryptic and cyanogen bromide digests of the latent protease chain of HPg. Confirmation of the presence of organic phosphate in the identified peptide was obtained by determination of the resulting mass shift after treatment of the peptide with alkaline phosphatase. The data show that Ser578 is a major phosphorylation site in HPg.
authors.affiliation: Department of Chemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.forename: M
authors.initials: M
authors.lastname: Prorok
authors.forename: R K
authors.initials: RK
authors.lastname: Bretthauer
authors.forename: F J
authors.initials: FJ
authors.lastname: Castellino
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010710:Phosphates / Q000032:analysis; D010766:Phosphorylation; D010768:Phosphoserine / Q000097:blood* / Q000737:chemistry*; D010958:Plasminogen / Q000737:chemistry* / Q000378:metabolism*; D012694:Serine / Q000097:blood* / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D010710:Phosphates; D010768:Phosphoserine; D012694:Serine; D010958:Plasminogen