title: Localization of phosphoserine residues in the alpha subunit of rabbit skeletal muscle phosphorylase kinase.
abstract: The alpha subunit of skeletal muscle phosphorylase kinase, as isolated, carries phosphate at the serine residues 1018, 1020 and 1023. Employing the S-ethyl-cysteine method, these residues are found to be phosphorylated partially, i.e. differently phosphorylated species exist in muscle. Serine 1018 is a site which can be phosphorylated by the cyclic-AMP-dependent protein kinase. The serine residues 972, 985 and 1007 are phosphorylated by phosphorylase kinase itself when its activity is stimulated by micromolar concentrations of Ca2+. These phosphorylation sites are not identical to those found to be phosphorylated already in the enzyme as prepared from freshly excised muscle. A 'multiphosphorylation loop' uniquely present in this but not in the homologous beta subunit contains all the phosphoserine residues so far identified in the alpha subunit.
authors.affiliation: Abteilung für Biochemie Supramolekularer Systeme, Ruhr-Universität Bochum, Federal Republic of Germany.
authors.forename: H E
authors.initials: HE
authors.lastname: Meyer
authors.forename: G F
authors.initials: GF
authors.lastname: Meyer
authors.forename: H
authors.initials: H
authors.lastname: Dirks
authors.forename: L M
authors.initials: LM
authors.lastname: Heilmeyer
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000302:isolation & purification; D000818:Animals; D001665:Binding Sites; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009132:Muscles / Q000201:enzymology*; D010446:Peptide Fragments / Q000302:isolation & purification; D010447:Peptide Hydrolases; D010710:Phosphates / Q000302:isolation & purification; D010764:Phosphorylase Kinase / Q000302:isolation & purification*; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis*; D011817:Rabbits; D012694:Serine / Q000031:analogs & derivatives*
chemical_list: D000596:Amino Acids; D010446:Peptide Fragments; D010710:Phosphates; D010768:Phosphoserine; D012694:Serine; D010764:Phosphorylase Kinase; D010447:Peptide Hydrolases