Membrane Signal Transduction via Protein Kinase C
Protein kinase C (PKC) is thought to play an important role in the signal transduction across the cell membrane in different cell types (Nishizuka 1984). Many different activators act via this pathway. PKC is activated by diacylglycerols that are produced by a phospholipase C as a consequence of the binding of an activator to a receptor. The activated PKC then phosphorylates intracellular substrates, which lead to the responses of the cell to the extracellular activator (Fig. 1). On the other hand, purified PKC binds phorbol esters, substances which have been known for many years as tumor promoters and nonphysiological cell activators (Hecker and Schmidt 1974). PKC is a Ca2+-activated, phospholipid-dependent enzyme and is modulated by phorbol esters and diacylglycerols: they activate PKC by lowering the amount of Ca2+ and phosphatidylserine needed for maximal activity (Castagna et al. 1982). The binding of radioactive phorbol esters can be inhibited competitively by diacylglycerols (Sharkey et al. 1984, Sharkey and Blumberg 1985), suggesting that diacylglycerol and phorbol esters have the same binding site.
KeywordsPhorbol Ester Sodium Pyrophosphate Membrane Signal Transduction DEAE Sephacel Chromatography Purify Protein Kinase
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