Localization of phosphoserine residues in the alpha subunit of rabbit skeletal muscle phosphorylase kinase |
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Authors: | H E Meyer G F Meyer H Dirks L M Heilmeyer |
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Affiliation: | Abteilung für Biochemie Supramolekularer Systeme, Ruhr-Universit?t Bochum, Federal Republic of Germany. |
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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. |
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