Phosphoenolpyruvate‐dependent protein kinase activity in rat skeletal muscle

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Abstract
Phosphoenolpyruvate‐dependent protein kinase activity has been demonstrated in the soluble fraction of rat skeletal muscle. The reaction was not due to the formation of ATP in the incubation mixture. Cyclic AMP, calcium, ATP and a number of phosphate acceptor proteins did not stimulate the reaction. One 32P‐labelled protein (M r 25 000) was observed on SDS gels. The phosphorylated protein contained acid stable phosphoserine as a major phosphorylated amino acid. The phosphorylation reaction in crude extracts was not directly proportional to the amount of protein, but typical of a two‐component system; i.e., kinase and substrate. The chromatography of soluble proteins on Ultrogel AcA44 separated the phosphate acceptor protein(s) from the phosphoenolpyruvate‐dependent protein kinase activity.