Cyclic guanosine monophosphate

Structural formula
General
Surname	Cyclic guanosine monophosphate
other names	Guanosine 3 ′, 5 ′ monophosphate cyclic GMP cyclo-GMP cGMP
Molecular formula	C 10 H 12 N 5 O 7 P
Brief description	colorless solid
External identifiers / databases
CAS number 7665-99-8 EC number 231-641-6 ECHA InfoCard 100.028.765 PubChem 24316 ChemSpider 22734 DrugBank DB02315 Wikidata Q422511
properties
Molar mass	345.21 g mol −1
Physical state	firmly
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 315-319-335 P: 261-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Cyclic guanosine monophosphate (short cyclic GMP , cyclo-GMP or cGMP ) is a second messenger , a cellular messenger substance that is responsible for the transmission of signals in the cell ( signal transduction ). As such he is u. a. in the visual process in the rods and cones of the retina, of the relaxation of the smooth muscle of the blood vessels of the regulation and insulin levels involved. Most of its effects in signal transduction cGMP presumably exerts via the cGMP-dependent protein kinase (protein kinase G).

Biosynthesis and degradation

cGMP is formed from guanosine triphosphate (5′-GTP), an ATP analog. There are at least two forms ( isoenzymes ) of guanylyl cyclase for this conversion

• one is stored in the plasma membrane and is stimulated by the hormones atrial natriuretic peptide (ANP) and BNP . The hormone binding site points outwards, the cGMP-forming domain inwards.
• the other is in the cytosol of certain cells. It is a heme protein that is activated by nitric oxide (NO). While the duration of action of NO (through oxidation) is limited, its release from nitroglycerin is a slow process.

The cGMP signal is terminated by a phosphodiesterase , which hydrolyzes the second messenger to guanosine monophosphate (5'-GMP).

function

Which signal is conveyed depends on the tissue:

• in the kidneys and intestines, it regulates ion transport
• in the smooth muscles it signals relaxation and thus leads, for example, to an expansion of blood vessels ( vasodilation ) and an expansion of the bronchi
• in the visual cells (rods) it increases the influx of sodium ions (Na ⁺ ) through sodium channels
• Insulin seems to regulate the cAMP and cGMP levels in opposite directions: the cAMP concentration decreases while that of the cGMP increases
• cGMP may be involved in the development of brain functions

See

Cyclic guanosine monophosphate is an important messenger substance in visual signal transduction . If little light falls on the light-sensing cells, they have a high cGMP concentration. This leads to a constant opening of cGMP-controlled ion channels in their cell membrane. As a result, the light sensory cell has a reduced membrane potential and its neurotransmitter, glutamate , is constantly released. This in turn leads to a constant activation of the downstream bipolar and ganglion cells with off-center.

When there is increased incidence of light on the light-sensing cells concerned, there is a structural change in the light-sensitive protein rhodopsin . This structural change leads to the activation of phosphodiesterases via an intermediate step. Phosphodiesterases are enzymes that break down cGMP. As a result of the falling cGMP level, the ion channels close, less glutamate is released and the downstream nerve cells with off-center are less strongly excited.

In the case of the downstream nerve cells (bipolar and ganglion cells) with an on center, the process is reversed.

See also

• cyclic adenosine monophosphate (cAMP)

Individual evidence

1. ↑ ^{a b c} data sheet guanosine 3 ′, 5′-cyclic monophosphate from Sigma-Aldrich , accessed on March 23, 2011 ( PDF ).