Abstract
It is now well established that post-translational modification of vertebrate cell proteins can occur by phosphorylation at serine, threonine, and tyrosine. Many serine- and threonine-speciflc protein kinases and their substrates have been extensively characterized, and in several instances protein phosphorylation has been shown to play an important role in the regulation of cell metabolism through alteration of the properties of specific enzymes. Historically, evidence that modulation of protein function led to a significant change in metabolism often predated the discovery that the protein in question was a phosphoprotein and the isolation of the regulatory protein kinase. For example, increased glycogenolysis in liver slices, under conditions of adrenaline or glucagon treatment, was correlated with activation of the enzyme glycogen phosphorylase. The active form of glycogen phosphorylase was subsequently found to be a phosphoprotein, and the protein kinase responsible, phosphorylase kinase, was characterized (Krebs and Fischer 1956). The regulation of phosphorylase kinase itself by phosphorylation has since been elucidated in great detail (Cohen 1978).
Published Version
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