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Topic: Purine


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In the News (Sun 17 Dec 17)

  
  Purine - Wikipedia, the free encyclopedia
Purines are biochemically significant as components of DNA and RNA, and are also found in a number of other important biomolecules, such as ATP, GTP, cyclic AMP, NADH, and coenzyme A.
Purines are biologically synthesised as nucleosides (bases attached to ribose).
Purines from food (or from tissue turnover) are metabolised by several enzymes, including xanthine oxidase, into uric acid.
en.wikipedia.org /wiki/Purine   (386 words)

  
 Encyclopedia: Purine
Purine and pyrimidine ribo- and deoxyribonucleotides may be synthesised de novo from simple molecules by energetically expensive, multistep pathways.
It is equally noteworthy that for both purine and pyrimidine metabolism, direct interconversions of the aminated nucleosides (adenosine, cytidine) with the corresponding bases (adenine, cytosine), or deamination at the base level, occur only in microorganisms and not in man. These differences are important for the design of effective antibiotic therapy.
For instance, a considerable amount of adenosine is produced endogenously (14-23 mmol/24 h in adults) as a by-product of the S-adenosylmethionine methylation pathway, a fraction of this being compartmentalised by protein binding.
www.nationmaster.com /encyclopedia/Purine   (1323 words)

  
 Purine anabolism
Purine can be synthesized from basic precursors: glycine, glutamine, aspartate, formate, and CO On completion of the purine ring, inosinic acid is produced, which is then converted to either adenosine nucleotide(AMP) or guanosine nucleotides(GMP).
The enzymes involved in the purine salvage processes are widely distributed in the body and may be important in providing purine ribonucleotides in tissues such as the brain that have a high turnover of purines but a limited capacity for their de novo synthesis.
The cost of synthesis of purines by the salvage processes is far lower than that for the de novo process: formation of one mole of purine mononucleotide formed by salvage requires 2 ATP whereas adenylic or guanylic acid synthesis requires 7 or 8 ATP, respectively.
www.iaea.org /programmes/nafa/d3/purine-cd/html/techdoc/html/02_3.htm   (392 words)

  
 Purine: Just the facts...   (Site not responding. Last check: 2007-09-18)
Other notable purines are xanthine (Crystalline oxidation product of the metabolism of nucleoproteins; precursor of uric acid; found in many organs and in urine), hypoxanthine (additional info and facts about hypoxanthine), theobromine (additional info and facts about theobromine), and caffeine (A bitter alkaloid found in coffee and tea that is responsible for their stimulating effects).
Purines are biologically synthesized as nucleotide (A phosphoric ester of a nucleoside; the basic structural unit of nucleic acids (DNA or RNA)) s (bases attached to ribose (A pentose sugar important as a component of ribonucleic acid)).
Purine (Any of several bases that are derivatives of purine) was named by the German (A person of German nationality) chemist (A scientist who specializes in chemistry) Emil Fischer (additional info and facts about Emil Fischer) in 1884.
www.absoluteastronomy.com /encyclopedia/p/pu/purine.htm   (424 words)

  
 Purine Research Society
When we consider the many different roles purines play in our metabolism, it is not surprising that the diseases of purine metabolism are as varied, ranging from asymptomatic conditions, which are only discovered accidentally, to disorders with severe neurological abnormalities, which are ultimately fatal.
One of the better known diseases of purine metabolism is caused by a deficiency of HPRT (enzyme 21).
Adenosine Deaminase (ADA) and Purine Nucleoside Phosphorylase (PNP) Deficiency.
www.purineresearchsociety.org   (2242 words)

  
 PURINES AND PYRIMIDINES
Purine and pyrimidines from tissue turnover which are not salvaged are catabolized and excreted.
In summary, all, except ring-methylated, purines are deaminated (with the amino group contributing to the general ammonia pool) and the rings oxidized to uric acid for excretion.
Since the purines are synthesized as the ribonucleotides, (not as the free bases) a necessary prerequisite is the synthesis of the activated form of ribose 5-phosphate.
www-medlib.med.utah.edu /NetBiochem/pupyr/pp.htm   (3844 words)

  
 Search Results for Purines - Encyclopædia Britannica
The purine ribonucleotides (AMP and GMP) are derived from ribose 5-phosphate.
Although the purine compounds cannot be classed as true pigments—they characteristically occur as white crystals—they often contribute to the general colour patterns in lower vertebrates and...
a compound belonging to the purine group, and the chief form in which nitrogen, resulting from the breakdown of protein during digestion, is excreted by reptiles and birds.
www.britannica.com /search?query=Purines&ct=   (459 words)

  
 Regulation of purine metabolism
Purine nucleotides produced from any of the input processes, including the de novo synthesis and salvage of either the endogenous or exogenous purines, could be converted into nucleotides of other purines.
The effect on the de novo purine synthesis is manifested in two ways: firstly a depressed activity of PRPP aminotransferase (EC.3.4.4.14), the enzyme that catalyses the first reaction of the de novo synthesis.
Since this enzyme could be inhibited by the feed-back of various purine nucleotides, with ATP and ADP being the most potent inhibitors, and secondly, a reduced supply of a substrate, PRPP (S-phosphoribosyl-1-pyrophosphate), the common substrate for both de novo and salvage pathways.
www.iaea.org /programmes/nafa/d3/purine-cd/html/techdoc/html/02_4.htm   (498 words)

  
 purine --  Encyclopædia Britannica
Purine is not common, but the purine structure occurs in many natural substances.
Although the purine compounds cannot be classed as true pigments—they characteristically occur as white crystals—they often contribute to the general colour patterns in lower vertebrates and invertebrates.
That purines are excretory materials is illustrated by the uric acid (or urates) and guanine found in the excrement of birds and of uric acid found in that of reptiles.
www.britannica.com /eb/article-9061952   (559 words)

  
 Purine and pyrimidine metabolic pathways   (Site not responding. Last check: 2007-09-18)
The latter is less expensive energetically and exerts feedback control on the former, thus restricting de novo synthesis to the minimum required to replace endogenous base irrevocably lost daily; in the case of purines, in the form of uric acid (2-3mmol/24 h).
In man, purine salvage takes place at the base level whilst pyrimidine salvage occurs at the nucleoside level; the reverse being true for microorganisms.
An example is the human erythrocyte, which lacks adenylosuccinate synthetase and thus cannot use synthesis or salvage to maintain its ATP levels, requiring adenosine for this [Stone and Simmonds, 1991].
www.amg.gda.pl /~essppmm/metabolism.html   (480 words)

  
 Purine and pyrimidine disorders   (Site not responding. Last check: 2007-09-18)
The function of purine and pyrimidine metabolism is to maintain the supply of these basic components to the different nucleotide pools, largely through an extremely efficient mechanism involving the degradation and recycling of the daily waste products of normal cell turnover, derived during red cell senescence, muscle work, wound healing, etc.
The first inherited purine disorder, xanthine dehydrogenase deficiency, was reported as a clinical entity in 1954.
The importance of the normal recycling of purine bases to the feedback control of purine synthesis is demonstrated by the gross overproduction found in the disorders where this is defective: hypoxanthineguanine phosphoribosyltransferase (HPRT) deficiency, aberrant phosphoribosylpyrophosphate synthetase (PRPS) activity, purine nucleoside phosphorylase (PNP) and adenylosuccinase (ADS) deficiencies.
www.amg.gda.pl /~essppmm/disorders.html   (1299 words)

  
 Purine - EvoWiki   (Site not responding. Last check: 2007-09-18)
Purines are one of two categories of organic base found in nucleic acids.
The purines found in nucleic acids are adenine and guanine, though there are other purines used elsewhere in the body.
Purines are larger molecules than pyrimidines, containing both six and five member nitrogen/carbon rings.
wiki.cotch.net /index.php/Purines   (203 words)

  
 Purine Biosynthesis. Big in Cell Division, Even Bigger in Nitrogen Assimilation -- Smith and Atkins 128 (3): 793 -- ...
for purine alkaloids, and for the adenine moiety of cytokinin
Genes encoding the enzymes of the purine pathway are shown in parentheses beneath the enzyme abbreviation.
The purines are oxidized within the infected cell cytosol to urate that is transferred to uninfected cells (UC) of the central zone and further oxidized within enlarged microbodies (Mb) to allantoin and allantoic acid (ureides).
www.plantphysiol.org /cgi/content/full/128/3/793   (5146 words)

  
 YLR209c Encodes Saccharomyces cerevisiae Purine Nucleoside Phosphorylase -- Lecoq et al. 183 (16): 4910 -- The Journal ...
Purine salvage is a complex pathway allowing interconversion of bases, nucleosides, and nucleotides.
Ylr209cp was unable to metabolize the purine nucleosides adenosine and xanthosine or the pyrimidine nucleosides uridine and
Phosphorolysis and hydrolysis of purine ribosides by enzymes from yeast.
jb.asm.org /cgi/content/full/183/16/4910   (1572 words)

  
 NEJM -- Abnormal purine metabolism and purine overproduction in a patient deficient in purine nucleoside phosphorylase
To delineate the normal function of purine nucleoside phosphorylase and to understand the pathogenesis of the immune dysfunction associated with deficiency of this enzyme, we studied purine metabolism in a patient deficient in purine nucleoside phosphorylase, her erythrocytes and cultured fibroblasts.
She exhibited severe hypouricemia and hypouricosuria but excreted excessive amounts of purines in her urine, the major components of which were inosine and guanosine.
Purine nucleoside phosphorylase is a necessary component of the major, if not the sole, pathway for the conversion of purine nucleosides and nucleotides to uric acid.
content.nejm.org /cgi/content/abstract/295/26/1449   (332 words)

  
 Purine and Pyrimidine Metabolism
Remember that the 2 purine bases are adenine and guanine and the pyrimidines are cytosine, thymine (in DNA), and uracil (in RNA).
The synthesis of the purine ring occurs on the ribose ring.
In addition to being a precursor for purine biosynthesis, PRPP is used in the biosynthesis of pyrimidine nucleotides and in the synthesis of histidine.
www.db.uth.tmc.edu /faculty/alevine/1521_2000/pursyn.htm   (1080 words)

  
 Purine salvage to adenine nucleotides in different skeletal muscle fiber types -- Brault and Terjung 91 (1): 231 -- ...
Purine salvage rates differ modestly, but significantly, among skeletal muscle fiber types (Table 1).
(35), and is tempered in deference to purine salvage (Fig.
Purine synthesis de novo and salvage in hypoxanthine phosphoribosyltransferase-deficient mice.
jap.physiology.org /cgi/content/full/91/1/231   (4863 words)

  
 PURINE DERIVATIVE EXCRETION BY HOLSTEIN COWS ABOMASALLY INFUSED WITH INCREMENTAL AMOUNTS OF PURINE   (Site not responding. Last check: 2007-09-18)
It has long been known that the excretion of purine derivatives (compounds arising from digestion of the purine components of DNA and RNA in microbial cells) was related to microbial protein supply in sheep.
Each day incremental amounts of purine were infused into the abomasum (the last compartment of the cow's stomach) and the corresponding excretion of purine derivatives in the milk and urine was measured.
Therefore, purine flow can be calculated from purine derivative excretion in the milk and urine and, after determining the protein:purine ratio of rumen microbes, microbial protein flow can then be estimated.
www.nal.usda.gov /ttic/tektran/DATA/000007/04/0000070456.html   (342 words)

  
 PURINE   (Site not responding. Last check: 2007-09-18)
imageimage A purine is a bicyclic organic compound, consisting of a fused pyrimidine/imidazole ring.
Purines from food are metabolized by several enzymes, including xanthine oxidase, into uric acid.
It is licensed under the GNU free documentation license.
www.yotor.org /wiki/en/pu/Purine.htm   (166 words)

  
 Nucleotide Metabolism
The purine base is built upon the ribose by several amidotransferase and transformylation reactions.
This is the enzyme responsible for converting adenosine to inosine in the catabolism of the purines.
The methyl group (recall that thymine is 5-methyl uracil) is donated by tetrahydrofolate, similarly to the donation of methyl groups during the biosynthesis of the purines.
web.indstate.edu /thcme/mwking/nucleotide-metabolism.html   (2966 words)

  
 Nucleotide Metabolism
The free purine bases---adenine, guanine, and hypoxanthine---can be reconverted to their corresponding nucleotides by phosphoribosylation.
Clinical manifestations of abnormal purine catabolism arise from the insolubility of the degradation byproduct, uric acid.
This is the compound responsible for converting adenosine to inosine in the catabolism of the purines.
www.med.unibs.it /~marchesi/nucmetab.html   (2942 words)

  
 Influence of Purine Intake on Uric Acid Excretion in Infants Fed Soy Infant Formulas -- Kuchan et al. 19 (1): 16 -- ...
purines as urinary uric acid was nearly quantitative [5] and
Ninety-eight percent of the purines in the STD Purine
Van Acker KJ, Eyskens FJ, Verkerk RM, Scharpe SS: Urinary excretion of purine and pyrimidine metabolites in the neonate.
www.jacn.org /cgi/content/full/19/1/16   (3668 words)

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