Second messengers cyclic GMP

Guanylyl cyclases (GC) are a family of enzymes (EC 4.6.1.2) that catalyse the formation of the second messenger cyclic GMP (cGMP) from guanosine triphosphate (GTP). GCs are subdivided in soluble GCs and GCs that are membrane-bound and linked to a receptor. Activation occurs by nitric oxide (NO) and pqrtide hormones, respectively [1,2]. 

A number of the actions of NO in target cells may be explained by its binding to the haem-containing protein soluble guanylyl cyclase (sGC), an enzyme which generates a second messenger, cyclic GMP (cGMP) from GTP. 

For the receptors that bind atrial natriuretic peptides and the peptides guanylin and uroguanylin, the intracellular domain is not a protein kinase but rather a guanylyl cyclase that synthesizes the second messenger cyclic guanosine monophosphate (cyclic GMP), which activates a cyclic GMP-dependent protein kinase (PKG) and can modulate the activities of several cyclic nucleotide phosphodiesterases, among other effectors. 

There are numerous second messenger systems such as those utilizing cyclic AMP and cyclic GMP, calcium and calmodulin, phosphoinosiddes, and diacylglerol with accompanying modulatory mechanisms. Each receptor is coupled to these in a variety of ways in different cell types. Therefore, it can be seen that it is impractical to attempt to quantitatively define each stimulus-response mechanism for each receptor system. Fortunately, this is not an... 

Cyclic nucleotides (cAMP and cGMP) are formed enzymatically from the corresponding triphosphates. As ubiquitous second messengers, they mediate many cellular functions which are initiated by first (extracellular) messengers. Their prime targets in eucaryotic cells are protein kinases ( cyclic AMP-dependent protein kinase, cyclic GMP-dependent protein kinase), ion channels and ensymes. 

The enzyme guanylyl cyclase produces the second messenger guanosine monophosphate (3, 5 -cyclic GMP, cGMP) from guanosine triphosphate (GTP). 

The mechanisms by which cyclic GMP produces its physiological effects are more varied. It has been more difficult to identify second messenger actions of cGMP compared to cAMP. This probably reflects the lower concentrations of cGMP in most tissues and the likelihood that cGMP plays a less widespread role in cell function. 

G-proteins are so called because they bind a guanosine nucleotide, either GTP or GDP. Their transduction mechanism involves the production of a second messenger such as 3 5 cAMP, 3 5 cyclic GMP (cGMP) or IP3 and diacylglycerol (DAG), derived from AMP, GMP and phosphatidyl inositol-3,5bisphosphate respectively (Figure 4.15). It is the second messenger that initiates the downstream amplification process phase of transduction. 

The biochemical cause(s) of erectile dysfunction is not known but one possibility is a low concentration of cyclic GMP in the smooth mnscle. On the basis of the principle of the regulation of second messengers see Chapter 12 and Box 12.2, the following might be responsible for a low... 

Inhibition of cyclic nucleotide phosphodiesterases is widely accepted as the predominant mechanism by which theophylline produces bronchodilation. Phosphodiesterases are enzymes that inactivate cAMP and cyclic guanosine monophosphate (GMP), second messengers that mediate bronchial smooth muscle relaxation. 

Second Law of Thermodynamics 284285 Second messengers 553 calcium ions 555 cyclic ADP-ribose 555 cyclic AMP 555 cyclic GMP 555... 

Most membrane receptors generate a diffusible intracellular signal called a second messenger. Five intracellular messengers are currently known Cyclic AMP, cyclic GMP, inositol triphosphate, diacylglyc-erol, and calcium. Second messengers usually activate or inhibit the action of one or more enzymes. 

There has been some work on the nature of the second messengers that mediate the mitogenic actions of prolactin on the crop sac. A role for cyclic GMP has been suggested [100]. Injection of this nucleotide with a small quantity of prolactin into the skin above the crop potentiated the actions of the hormone, although when injected alone the cyclic nucleotide had no effect. 

The cyclic nucleotides adenosine 3, 5 -cyclic monophosphate (cyclic AMP (cAMP)) and guanosine 3, 5 -cyc.lic monophosphate (cyclic GMP (c.GMP)) are second messengers generated by adenylyl (adenylate) cyclase (AC) and guanylyl (guanylate) cyclase (GC), respectively, in response to receptor occupation by particular primary messengers , that is,... 

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