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Uric acid

life science Maturity 11-13 Next article →

Uric acid is a complex chemical compound made of carbon, nitrogen, oxygen, and hydrogen. Its chemical formula is C5H4N4O3. This substance is a natural byproduct of the body breaking down purine nucleotides. In the human body, it usually exists as the urate ion, which is a conjugate base.

Urat
Urat

Uric acid is vital because it acts as a powerful antioxidant. In human blood plasma, more than half of the antioxidant capacity comes from the hydrogen urate ion. This helps protect cells from damage. However, if levels in the blood become too high, it can lead to medical issues like gout or kidney stones.

The production of uric acid follows a specific biological pathway. It begins with the breakdown of purines into substances called hypoxanthine and xanthine. An enzyme called xanthine oxidase (XO) then catalyzes the conversion of these substances into uric acid.

Harnsäure Ketoform
Harnsäure Ketoform

This enzyme is quite large and contains a metal called molybdenum bound to sulfur and oxygen. While its name suggests it acts as an oxidase, it mostly functions as a dehydrogenase. In some cases, diet can change this process. For example, consuming excessive fructose can trigger an unregulated pathway. This pathway consumes ATP and converts fructose into fructose-1-phosphate, which eventually leads to the degradation of AMP into uric acid.

Uric acid behaves differently depending on the species of animal. In most mammals, an enzyme called uricase further breaks down uric acid into a substance called allantoin. Humans and other higher primates have lost this uricase enzyme. Because of this, uric acid is the final breakdown product of purine metabolism in humans. Some scientists believe that in primates, urate may partially substitute for vitamin C, which is also a strong antioxidant. Other animals use uric acid for different survival needs. Birds, reptiles, and some desert mammals, like the kangaroo rat, excrete uric acid as a dry mass in their feces. This process is energetically expensive, but it prevents dehydration by reducing water loss.

Even different breeds of animals show unique genetic traits regarding this compound. For instance, Dalmatian dogs have a genetic defect in how their liver and kidneys take up uric acid. This defect prevents them from converting it to allantoin, so they excrete uric acid instead. In the world of invertebrates, the marine worm *Platynereis dumerilii* uses uric acid for communication. The female releases the acid into the water as a sexual pheromone. This chemical signal induces males to release sperm, helping the species reproduce.

History shows how much we have learned about this molecule. In 1776, a Swedish chemist named Carl Wilhelm Scheele first isolated uric acid from kidney stones. This was a major step in understanding metabolic waste. Later, in 1882, Ukrainian chemist Ivan Horbaczewski successfully synthesized the compound. He achieved this by melting urea with glycine. These discoveries allowed scientists to study the chemical structure and the way it crystallizes in the lactam form.

Understanding the solubility of uric acid is crucial for medicine. Generally, uric acid and its salts have low water solubility. This low solubility is a key factor in the development of gout. For example, it takes 15,000 grams of cold water to dissolve just one gram of uric acid. However, it is much more soluble in hot water.

Urine crystals comparison
Urine crystals comparison

In humans, the kidneys handle about 70% of daily uric acid disposal. A normal daily excretion in urine is between 270 and 360 mg. If the kidneys do not excrete it properly, a person may develop hyperuricemia, which means high levels of uric acid in the blood.

High levels of uric acid can cause serious health conditions. Gout is a painful condition where monosodium urate crystals form in joints and tissues. These crystals are often described as needle-like.

Urine crystals comparison
Urine crystals comparison

Another serious concern is Tumor Lysis Syndrome. This occurs when cancer cells break down rapidly, releasing their contents into the blood. This can cause uric acid levels to spike, potentially leading to acute kidney injury. Doctors treat these high levels using methods like hyperhydration or medicines like allopurinol, which inhibits the enzyme xanthine oxidase to slow down production.

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File:Harnsäure Ketoform.svg
Harnsäure Ketoform.svg
File:Urat.svg
Urat.svg
File:Urine crystals comparison.png
Urine crystals comparison.png
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