Purine is a water-soluble heterocyclic aromatic organic compound consisting of a six-membered pyrimidine ring and a five-membered imidazole ring.
A nucleotide sequence in the cell’s DNA determines the nucleotide sequence of each RNA and the amino acid sequence of each protein.
Nucleotides have three characteristic components:
- A nitrogenous (nitrogen-containing) base
- A pentose
- A phosphate
The nitrogenous bases are derivatives of two parent compounds, pyrimidine, and purine.
- Nine atoms make up the basic purine structure.
- A six-membered pyrimidine ring and a five-membered imidazole ring fused to make up the two cycles of purine.
- Four nitrogen atoms exist in positions 1, 3, 7, and 9.
- The first nitrogen of the six-membered ring serves as the starting point for purine’s numbering, which moves counterclockwise.
- The imidazole ring is numbered in a clockwise direction.
- Purine bases are attached with 1’ carbon of pentoses through the ninth nitrogen atom to form nucleosides.
- Significant delocalization exists among the purine ring’s electrons.
- Positions 3 and 7 are electron-rich and susceptible to electrophilic attack, while positions 2, 6, and 8 are susceptible to nucleophilic attack.
Types of Purine
The primary purines are adenine and guanine in both RNA and DNA.
Molecular formula: C5H5N5
Molecular weight: 135.13 dalton
Melting point: 360-365°C
Solubility: 1030 mg/L (at 25 °C)
- It is a white, crystalline purine base with an amine group linked to the carbon at position 6 that is present in both RNA and DNA.
- Thymine in DNA and Uracil in RNA is complementary to adenine.
- The amine group at position 6 and the additional double bond between N-1 and C-6 in the heterocyclic aromatic (pyrimidine) ring distinguish adenine from guanine.
- The energy-rich adenosine triphosphate (ATP) and the cofactors flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NAD), and coenzyme A are examples of adenine derivatives that play various roles in biochemistry, including cellular respiration.
Molecular formula: C5H5ON5
Molecular weight: 151.13 dalton
Melting point: 360°C
Solubility: 2080 mg/L (at 37 °C)
- It is a white, insoluble, crystalline material.
- It is a 2-aminopurine with a 6-oxo substituent in both RNA and DNA.
- Guanine is complementary to Cytosine in both DNA and RNA.
- It was first isolated from guano (bird manure), hence the name.
- Ammonia, a byproduct of protein breakdown in cells, is converted to guanine by spiders, scorpions, and a few other amphibians, as it can be eliminated with minimal water loss.
Aside from adenine and guanine, other significant metabolites include hypoxanthine, xanthine, theophylline, theobromine, caffeine, uric acid, and isoguanine.
- 3, 7-dimethylxanthine (theobromine) is a powerful diuretic and facilitates oral administration by forming soluble complexes with salts of different organic acids and also in treating asthma.
- The primary purine found in coffee beans and tea leaves is 1,2,7-trimethylxanthine (caffeine) which is a cardiac and respiratory stimulant and is frequently used in headache powders.
- The main purine component of human urine is 1-methylxanthine.
- 3- and 7-Methylpurines are also minor components of urine, particularly after consuming substantial amounts of caffeine or other methylated xanthines.
- Paraxanthine, also known as 1,7-Dimethylxanthine, is an effective diuretic with antithyroid effects.
- Numerous biologically active substances have been produced from modified purine structures, both of natural and synthetic origin.
- These substances often include simple alterations to known purines, such as cytokinins, 6-N-alkylated adenines, or structural changes to the carbohydrate moiety of ribose or deoxyribose derivatives, as with arabinosides.
- Methylation is the most common form of purine modification.
- Some modified purines can be found in transfer RNAs (tRNAs).
- Before the reverse shift to the B-supercoiled conformation, methylation of one of the two purines is presumably eliminated during the cell cycle.
- Methylation of purines (particularly of adenine) in DNA is known to occur in the genetic material of microorganisms. The 6-methyladenine is found in bacterial DNA.
Antibiotics and Related Compounds
Numerous glycosylpurines that have been extracted from microbes have shown significant biological activity.
- 9-(Darabinofuranosyl) adenine, often known as Ara A, is a potent antiviral and anticancer drug.
- Both bacterial and human cells have been thoroughly examined to determine the effects of puromycin as a protein production inhibitor. However, its use as an antibiotic is constrained by the fact that it is highly toxic to mammals.
- The ketosylpurines (psicofuranine and decoyinine) work by inhibiting XMP aminase exhibiting antibacterial efficacy and against adenocarcinoma in rats.
- Septacidin has some activity against tumor cells.
- Nebularine is known to show antibacterial properties.
- 6-Mercaptopurine (6-thioxo-l,6-dihydropurine) was among the first purine derivatives used in leukemia treatment, particularly in children.
- 2,6-diaminopurineare has anti-leukemic activity.
Purine Health Effects
- Uric acid is the metabolic end product of purine metabolism.
- Too much purine in the body can result in hyperuricemia, a condition when there is an excessive amount of uric acid in the blood.
- A higher risk of developing diabetes is associated with high uric acid levels in the body.
- High uric acid levels in the body are also known to cause the formation of uric acid crystals leading to gout (inflammation in the joint) and kidney stones.
- Dvir G., Benjamin A., Palmer B.A., Weiner S., & Addadi L. (2017). Light manipulation by guanine crystals in organisms: biogenic scatterers, mirrors, multilayer reflectors and photonic crystals. Advanced Functional Materials. 27 (6): 1603514. https://doi.org/10.1002/adfm.201603514
- Jain J.L., Jain S. & Jain N. (2005). Nucleic Acids. In Fundamentals of Biochemistry. Multicolour Illustrative Edition. S. Chand & Company Ltd, pg. 284-286
- Kumari A. (2018). Purine de novo Synthesis. In Sweet Biochemistry. Academic Press, pg. 93-97. https://doi.org/10.1016/B978-0-12-814453-4.00018-2
- Maas R. (2004). Prereplicative purine methylation and postreplicative demethylation in each DNA duplication of the Escherichia coli replication cycle. The Journal of biological chemistry, 279(49), 51568–51573. https://doi.org/10.1074/jbc.M407394200
- Nelson D. L. & Cox M.M. (2008). Nucleotides and Nucleic Acids. In Lehninger Principles of Biochemistry. Fifth Edition. W.H. Freeman and Company, pg. 271-274. ISBN-I0: 0-7167-7r08-X
- PubChem. Purine. National Library of Medicine. National Institutes of Health. Department of Health and Human Services, USA. Accessed from: https://pubchem.ncbi.nlm.nih.gov/compound/Purine. Accessed on: 14.09.2022
- PubChem. Adenine. National Library of Medicine. National Institutes of Health. Department of Health and Human Services, USA.
- Accessed from: https://pubchem.ncbi.nlm.nih.gov/compound/Adenine#section=Chemical-and-Physical-Properties. Accessed on: 14.09.2022
- PubChem. Guanine. National Library of Medicine. National Institutes of Health. Department of Health and Human Services, USA.
- Accessed from: https://pubchem.ncbi.nlm.nih.gov/compound/Guanine#section=Chemical-and-Physical-Properties. Accessed on: 14.09.2022
- Robert J., Ouellette J. & David Rawn. (2018). Nucleosides, Nucleotides, and Nucleic Acids. In Organic Chemistry (Second Edition). Academic Press, pg. 973-1000. https://doi.org/10.1016/B978-0-12-812838-1.50030-X.
- Shaw G. (1984). Purines. In Comprehensive Heterocyclic Chemistry. Pergamon. pg. 499-605. https://doi.org/10.1016/B978-008096519-2.00077-1
WebMD. (2022). Foods High in Purines. Accessed from: https://www.webmd.com/diet/foods-high-in-purines#1. Accessed on: 14.09.2022