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(gwä`nēn), organic base of the purinepurine,
type of organic base found in the nucleotides and nucleic acids of plant and animal tissue. The German chemist Emil Fischer did much of the basic work on purines and introduced the term into the chemical literature in the early 20th cent.
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 family. It was reported (1846) to be in the guanoguano
, dried excrement of sea birds and bats found principally on the coastal islands of Peru, Africa, Chile, and the West Indies. It contains about 6% phosphorus, 9% nitrogen, 2% potassium, and moisture. Guano is found mixed with feathers and bones and is used as a fertilizer.
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 of birds; later (1879–84) it was established as one of the major constituents of nucleic acidsnucleic acid,
any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis.
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. The accepted structure of the guanine molecule was proposed in 1875, and the compound was first synthesized in 1900. When combined with the sugar ribose in a glycosidic linkage, guanine forms a derivative called guanosine (a nucleoside), which in turn can be phosphorylated with from one to three phosphoric acid groups, yielding the three nucleotidesnucleotide
, organic substance that serves as a monomer in forming nucleic acids. Nucleotides consist of either a purine or a pyrimidine base, a ribose or deoxyribose, and a phosphate group. Adenosine triphosphate serves as the principle energy carrier for the cell's reactions.
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 GMP (guanosine monophosphate), GDP (guanosine diphosphate), and GTP (guanosine triphosphate). Analogous nucleosides and nucleotides are formed from guanine and deoxyribose. The nucleotide derivatives of guanine perform important functions in cellular metabolism. GTP acts as a coenzymecoenzyme
, any one of a group of relatively small organic molecules required for the catalytic function of certain enzymes. A coenzyme may either be attached by covalent bonds to a particular enzyme or exist freely in solution, but in either case it participates intimately in
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 in carbohydrate metabolism and in the biosynthesis of proteins; it can readily donate one of its phosphate groups to adenosine diphosphate (ADP) to form adenosine triphosphateadenosine triphosphate
(ATP) , organic compound composed of adenine, the sugar ribose, and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of
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 (ATP), an extremely important intermediate in the transfer of chemical energy in living systems. GTP is the source of the guanosine found in RNA and deoxyguanosine triphosphate (dGTP) is the source of the deoxyguanosine in DNA, and thus guanine is intimately involved in the preservation and transfer of genetic information. Guanine is said to account for the iridescence of fish scales and the white, shiny appearance of the skin of many amphibians and reptiles.



2-amino-6-oxypurine. a purine base, widely distributed in animal and plant cells (it is a constituent of nucleic acids and is present in a free state).

It is the main component of the excrements of spiders and birds and was discovered in guano (hence the name). A considerable amount of guanine is present in the scales and skin of fish, reptiles, and amphibians. The calcium compound of guanine gives fish scales their characteristic shine. In mammal organisms, guanine is transformed into xanthine under the action of the enzyme guanase.


C5H5ON5 A purine base; occurs naturally as a fundamental component of nucleic acids.
References in periodicals archive ?
Indirect evidence for the interaction between muscarinic receptors and G proteins is based on the observation that agonist but not antagonist binding to muscarinic receptors in membranes of rat heart is affected by GTP and GDP, (71) which is similar to the original effect of guanine nucleotides on the agonist binding to [beta] adrenergic receptors.
2] receptors are known to show high affinity for agonists when reconstituted with G proteins in the absence of guanine nucleotides, whereas they show low affinity for agonists in the absence of G proteins (74,77) (Fig.
In addition, the increased potency of guanine nucleotides observed in the solubilized preparation is consistent with recent reports of similar changes in the neuropeptide Y and somatostatin receptors (Marie et al.
Differential regulation by guanine nucleotides of opiate agonist and antagonist interactions.

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