Cell function intracellular signal transduction

Specialized cells such as neurons and muscle cells are electrically excitable and controlled by transmitter and modulator substances. Chemicals can affect the regulation of the activities of such cells. This can occur by (i) alterations in a neurotransmitter, (n) receptor function, (Hi) intracellular signal transduction, or (iv) signal-terminating processes. 

Intracellular proteins that bind GTR and have a wide variety of functions including signal transduction and in turn protein synthesis and cell proliferation. These proteins are active when GTR is bound on hydrolysis of the GTR to GDR, activity is lost. See Rouot, B., Brabet, R, Homberger, V. et al., Go, a major brain GTR-binding protein in search of a function purification, immunological, and biochemical characterization, Biochimie 69,339-349,1987 Obar, R.A., Shpetner, H.S., and Vallee, R.B., Dynamin ... 

Binding of extracellular signaling molecules to cell-surface receptors triggers Intracellular signal-transduction pathways that ultimately modulate cellular metabolism, function, or gene expression (Figure 13-1). 

In addition to cell-surface receptors and second messengers, two groups of evolutionary conserved proteins function in signal-transduction pathways stimulated by extracellular signals. Here we briefly consider these Intracellular signaling proteins their role in specific pathways is described elsewhere. 

Most G proteins are heterotrimers consisting of a, P and y subunits which function in close association with several transmembrane receptors. Their activity is regulated by the binding of GTP to the a subunit, followed by subsequent hydrolysis of GTP to GDP, and release of GDP (41). Functions regulated by G proteins include stimulation of phosphoinositide hydrolysis, modulation of adenylate cyclase activity and activity of ion channels (41). Therefore, G proteins play a crucial role in relaying information from cell surface receptors to the intracellular signal-transduction machinery. 

A great deal of attention has been paid to the direct interaction of metal complexes with DNA, somewhat less to interactions with RNA, and much, much less to other potential modes of affecting cell function. In contrast most existing therapeutic agents act on cell surface receptors, membrane transport proteins, intracellular signal transduction cascades, and nuclear receptor proteins, or as inhibitors of metabolic enzymes. Additional research in these latter areas is particularly needed. 

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