J. Biol. Chem., Vol. 256, Issue 17, 8871-8874, Sep, 1981
Phosphorylation of glycogen synthase and of the beta subunit of eukaryotic initiation factor two by a common protein kinase
AA DePaoli-Roach, PJ Roach, K Pham, G Kramer and B Hardesty
A protein kinase from rabbit reticulocytes, able to phosphorylate the beta
subunit of eukaryotic initiation factor 2 (eIF-2), has been demonstrated to
phosphorylate also glycogen synthase. A glycogen synthase kinase (PC0.7)
from rabbit skeletal muscle has been shown to phosphorylate the beta
subunit of eIF-2. Comparison of highly purified preparations of the two
protein kinases has indicated several similarities of properties. 1) Both
enzymes were associated with two major polypeptide species, alpha (Mr =
43,000) and beta (Mr = 25,000), and exhibited apparent native molecular
weights of 176,000-180,000 by gel filtration and 130,000-140,000 by sucrose
density gradient sedimentation. 2) Both enzymes phosphorylated glycogen
synthase, eIF-2 beta, phosvitin, and casein and were effective in utilizing
GTP and ATP as phosphoryl donors. 3) Both enzymes displayed the same
chromatographic behavior on phosvitin-Sepharose, phosphocellulose, and
DEAE-cellulose. 4) Both enzymes underwent an autophosphorylation of the
beta polypeptide when incubated with ATP and Mg2+. On the basis of these
and other properties, we propose that the two protein kinases, if not
identical, are very similar enzymes.
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