The G-Proteins Regulating Phosphoinositide Breakdown
The stimulation of phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis is a widespread cellular response to many hormones, growth factors and neurotransmitters (Berridge 1987). It is catalyzed by a phospholipase C (PLC) and yields two signaling molecules: inositol 1,4,5-trisphosphate (IP3) which releases Ca2+ from stores in the endoplasmic reticulum, and 1,2-diacylglycerol (DAG) which activates protein kinase C. The growth factors activate the PLC through the tyrosine kinase activity of their receptors (Kriz et al 1990), whereas the other agonists act through guanine nucleotide-binding regulating proteins (G-proteins). Despite the recognition several years ago that G-proteins were involved in the regulation of PLC, some of these G-proteins have only recently been identified (Taylor et al 1990, Smrcka et al 1991, Blank et al 1991). These G-proteins are insensitive to pertussis toxin, but it is clear that toxin-insensitive G-proteins are also involved in the regulation of PLC in some tissues (Exton 1988).
KeywordsHydrolysis Tyrosine Heparin Triphosphate Inositol
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