The Protein Kinase Family
An ever-expanding list of protein kinases is now known to serve diverse physiological roles in cellular systems (Table I). By phosphorylating serine, threonine or tyrosine residues in target proteins, these enzymes transduce metabolic or hormonal signals with profound cellular consequences (Krebs & Beavo, 1979; Flockhart & Corbin, 1982; Nishizuka, 1984; Stull et al., 1985). Serine- or threonine-specific protein kinases were first found to exercise control of diverse metabolic processes. Tyrosine-specific protein kinases are now found both as domains of trans-membrane growth factor receptors and encoded by viral oncogenes (Sefton & Hunter, 1985). Thus, some protein kinases are integral membrane proteins that are directly involved in the transduction of extracellular signals for intracellular purposes. Others act as amplifiers of intracellular signals, as regulators of structural or enzymatic components of cells, and as the unregulated products of certain oncogenic lesions.
KeywordsTyrosine Propane Serine Lysine Sarcoma
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