Identification of the sites on rabbit skeletal muscle protein phosphatase inhibitor-2 phosphorylated by casein kinase-II
- 22 April 1986
- journal article
- Published by Elsevier BV in Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology
- Vol. 870 (3), 408-416
- https://doi.org/10.1016/0167-4838(86)90248-7
Abstract
Inhibitor-2 was phosphorylated by casein kinase-II in vitro at a rate similar to that of glycogen synthase, a physiological substrate of this protein kinase. The major phosphorylation sites were identified as serines-86, -120 and -121, the peptide containing serines-120 and -121 being labelled about 2.5-fold more rapidly than that containing serine-86. The 13 residues C-terminal to serine-121 (SGEEDSDLSPEERE) contain seven acidic amino acids, while the six residues following serine-86 (SDTETTE) contain three. These results are consistent with the known specificity requirements of casein kinase-II. The three serines are C-terminal to the threonine (residue 72) whose phosphorylation by glycogen synthase kinase-3 is potentiated by prior phosphorylation with casein kinase-II. This reinforces the view that a C-terminal phosphoserine residue is important for the specificity of glycogen synthase kinase-3. Identification of the residues phosphorylated by casein kinase-II will facilitate further studies on the in vivo phosphorylation state of inhibitor-2.Keywords
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