Adenylate cyclase signal transduction

Normalizes or inhibits secondary messenger systems (e.g, inhibits phos-phoinositide and adenylate cyclase signaling normalizes guanine nucleotidebinding protein [G protein] signal transduction system) ... 

Fig. 5 Proposed signal transduction mechanisms that stimulate the pheromone biosynthetic pathway in Helicoverpa zea and Bombyx mori. It is proposed that PBAN binds to a G protein-coupled receptor present in the cell membrane that upon PBAN binding will induce a receptor-activated calcium channel to open causing an influx of extracellular calcium. This calcium binds to calmodulin and in the case of B. mori will directly stimulate a phosphatase that will dephosphorylate and activate a reductase in the biosynthetic pathway. In H. zea the calcium-calmodulin will activate adenylate cyclase to produce cAMP that will then act through kinases and/or phosphatases to stimulate acetyl-CoA carboxylase in the biosynthetic pathway...

Calcitonin lowers serum Ca2+ and Pi levels, primarily by inhibiting the process of bone resorption, but also by decreasing resorption of Pi and Ca2+ in the kidney. Calcitonin receptors are predictably found primarily on bone cells (osteoclasts) and renal cells, and generation of cAMP via adenylate cyclase activation plays a prominent role in hormone signal transduction. 

As noted, the labdanes display a broad spectrum of biochemical and pharmacological activities, suggesting that they may significantly affect the function of the immune system and inflammatory cells. The labdanes may affect critical enzymes such as adenylate cyclase, protein kinases and phospholipase A2, which are intimately involved in signal transduction and cell activation processes. Much of the information on labdane-type diterpene effects has been provided by forskolin and mainly in in vitro systems. 

These studies all support the hypothesis that external stimuli of the elicitor cause an increase in the cytoplasmic Ca2+ level via the phosphatidylinositol cycle and/or the adenylate cyclase system. Although an authoritative picture of this process cannot yet be given, possible signal transduction mechanisms are summarized in Fig. (2). At present the data... 

Signal transduction was studied most precisely for the 5-HTiA receptor in rat amygdala (Koyama et al. 1999). The receptor operated through a N-methyl maleimide-sensitive mechanism and by adenyl cyclase inhibition rather than any change in K+ or Ca2+ channels. The fall in cyclic AMP presumably was followed by decrease in the phosphorylation of synaptic vesicle proteins and, finally, in a decrease of exocytosis. 

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