Structural Biochemistry/Nucleic Acid/Nitrogenous Bases/Purines

== What is a Purine? ==

The name was invented by the German chemist Emil Fischer in 1884. A purine is a nucleotide (a nucleoside + phosphate group) that is amine based and planar, aromatic, and heterocyclic. The structure of purine is that of a cyclohexane(pyrimidine group) and cyclopentane(imidazole group) attached to one another; the Nitrogen atoms are at positions 1,3,7,9. Adenine(A) and Guanine(G) are examples of purines which are involved in the construction of the backbone of the DNA and RNA. They are also a part of the structures for Adenosine disphosphate (ADP), triphosphate(ATP), and other enzymes. Purines form bonds with pentoses exclusively through the 9th Nitrogen atom.

6-amino and 2-amino-6-oxy purine

One derivative form of purine, adenine (A), is also commonly known as 6-amino purine. The 6-amino purine molecule contains an amine group attached to the carbon atom at position 6 double bonded to the nitrogen atom at position 1 and single-bonded the carbon atom at position 5. Another derivative form of purine, guanine (G), is also known as 2-amino-6-oxy purine. The 2-amino-6-oxy purine contains an amine group attached to the carbon atom at position 2 double bonded to the nitrogen atom on position 3 and single-bonded to the nitrogen atom on position 1. Guanine also has a carbonyl group at position 6 hence the 6-oxy.

6-amino purine; Adenine

2-amino-6-oxy purine; Guanine. Arrows indicate direction of hydrogen bonding.

Purine content in foods

Food is responsible for approximately 30% of uric acid in the blood. Regular diets could affect the level of uric acid. Some food will increase the blood acidity even if the content in purine is low.

Lowest level of Purine: 0–50 mg

tea, coffee, soda, nuts, dairy products, vegetables, cereal, fruits, preserve foods, sweets

Moderate level of purine: 50–150 mg

spinach, avocado, beef, turkey, lamb, oyster, fish, peanuts, sausages, ducks, chickens

High level of purine: 150–1000 mg

kidney, liver, heart, caviar, scallops, lobster, sardines, Thai fish sauce

Risks

A diet high in purines can lead to gout, a form of arthritis with symptoms of severe pain, redness, and swelling. Uric acid is a product formed from the breakdown of purines. Uric acid builds up in one's joints, causing the inflammation and resultant pain.

2 Types of Purine Disorders of Nucleotide Synthesis

Adenylosuccinase deficiency

This causes retardation or heart attacks due to high level of succinyladenosine in urine. Currently, there is no treatment.

Phosphoribosylpyrophosphate synthetase superactivity

A recessive disorder which causes too much production of purines, which results in gout or other developmental effects. Treatments could include low purines in daily diet.

Functions

Purines are biochemically significant in a myriad of biomolecules besides DNA and RNA, such as ATP, GTP, cyclic AMP, NADH, and coenzyme A. Although purine has not been found naturally in nature, it can be produced through organic synthesis. Purines can also be used as neurotransmitters, acting upon purinergic receptors (i.e., adenosine activates adenosine receptors)

Metabolism

Many organisms utilize metabolic pathways in order to synthesize and break down purines. Biologically, purines are synthesized as nucleosides, which are bases attached to ribose.

Laboratory Synthesis

Purines can be created artificially, too, and not just through vivo synthesis in purine metabolism. When formamide is heated in an open vessel at 170°C for 28 hours, purine is obtained.

Procedure

1. Obtain a sample of formamide
2. Heat in an open vessel with a condenser for 28 hours in an oil bath at 170-190°C
3. Remove excess formamide through vacuum distillation
4. Reflux the residue with methanol
5. Filter the methanol solvent and remove by vacuum distillation