purine
Meaning of purine: Half the alphabet of the genetic code, and the reason uric acid builds up and triggers a gout attack.
Definition of purine
A purine is a nitrogen-containing compound built from two fused rings, and one of the two chemical families that supply the letters of the genetic code. Adenine and guanine are the purines found in DNA and RNA; the other family, the pyrimidines, has a single ring. The body dismantles purines into uric acid, which normally leaves in the urine.
What do purines do in the body?
Their best-known job is structural. Adenine and guanine pair with the single-ring bases across the two strands of DNA, and that reliable pairing is what allows the molecule to be copied faithfully. Purines do more than carry information. Adenine forms the core of ATP, the molecule cells use as portable energy, and of cyclic AMP, a messenger inside cells. Several vitamins and coenzymes contain a purine ring. Cells both build purines from scratch and salvage the parts of broken-down ones, because building them fresh costs a great deal of energy.
How are they broken down?
Old or surplus purines are dismantled in steps, ending at uric acid. Most mammals take one further step and convert uric acid into a more soluble compound that the kidneys clear easily. Humans lack the enzyme that does it. Uric acid is therefore the end of the line, and all of it must be excreted. That single missing enzyme is why gout is a human problem and almost unknown in most other mammals.
Which foods contain the most purines?
| Food | Purine content |
|---|---|
| Organ meats, anchovies, sardines | High |
| Red meat, shellfish, some fish | Moderate to high |
| Beer and spirits | Raise uric acid strongly |
| Dairy, eggs, most vegetables | Low |
The body's own cell turnover contributes more to blood uric acid than food does, so diet alone rarely explains a high level.
What happens when uric acid builds up?
When the level in blood stays high, uric acid can come out of solution and form needle-shaped crystals. In a joint, classically at the base of the big toe, those crystals set off a fierce inflammatory attack, which is what gout is. In the kidney they can build into stones. A raised level without symptoms is common and does not always progress. Rapid destruction of many cells at once, as when a large tumor responds to treatment, releases a flood of purines and can push uric acid up sharply.
Used in a sentence
The assessment of recurrent gout included a dietary history focused on purine intake.
Good to know
Humans lack the enzyme that converts uric acid into a more soluble product, so purine breakdown stops at uric acid and any excess must be excreted or it crystallizes.
Word origin
Where “purine” comes from
Coined from the Latin purum, meaning pure, and uricum, from uric acid, because the compound was first identified through work on uric acid.