Kinetics of calcium and calmodulin‐dependent protein kinase III from embryonic chicken leg muscle cells

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Abstract
Embryonic chicken muscle cells (CELM) contain the calmodulin‐dependent protein kinase that specifically phosphorylates eukaryotic elongation factor 2. The kinase requires Ca2+ and maximum activity in CELM was observed at 10 μM Ca2+. The ATP concentration required for half the maximum activity of CaM PKIII in CELM was calculated to be 0.15 mM. In CELM, dephosphorylation of eEF‐2 was catalyzed by phosphoprotein phosphatase PP2A alone. The activity of PP2A was relatively low and the half‐life of added phosphorylated eEF‐2 was more than 15 min. Due to the low phosphoprotein phosphatase activity, inhibition of the PP2A activity by addition of okadaic acid had little effect on the eEF‐2 phosphorylation kinetics.