Uric acid

  • 2,6,8 - trihydroxypurine ( enol form, left)
  • Purine -2, 6,8 (1H, 3H, 9H) -trione ( keto form, right)

Odorless pale beige solid

Fixed

1.89 g · cm -3

> 300 ° C

3.89 ( 12 ° C)

Little in water

Template: Infobox chemical / molecular formula search available

Uric acid (clinically common abbreviation " HS ", but not to be confused with urea) is the end product of nucleic acid degradation ( here: degradation of purine bases ) of many species of animals such as reptiles, birds, monkeys and humans. In reptiles and birds also amino acids are broken down into uric acid. The salts of uric acid are called urates.

Structure

Uric acid is constructed as 2,6,8 - trihydroxypurine of an aromatic six-membered ring, which is followed by a five-membered ring. In the ring structure substituted four nitrogen atoms, the carbon atoms 1, 3, 7 and 9 to the carbon atoms 2, 6 and 8 are hydroxy-( lactim form ) or oxo groups ( lactam ) bound.

Properties

Uric acid forms white, odorless crystals which melt at 300 ° C, and occurs in two tautomeric forms (see structural formula ). Uric acid is a weak acid only bad in the protonated state (eg, in water), however, is well soluble in basic media. The alkali metal salts (especially lithium) have a better water solubility.

Biological Significance

Physiology

In the organism of hominids, ie humans, chimpanzees, gorillas and orang- utans, uric acid formed as a breakdown product of purine bases and is the end product of purine metabolism. It arises from hypoxanthine or xanthine by the enzyme xanthine oxidase. Uric acid is the final breakdown product of purine nucleotides and is about 75% of renal, ie via the kidneys, excreted. In addition also takes place on an elimination saliva, sweat or intestinal secretion, ie through the intestines. The daily excretion of up to 1 g

In other mammals, uric acid is converted by the enzyme uricase in allantoin.

Although hominids uric acid can not further break down, they have in the kidney in the form of an effective Reabsorptionssystem uric acid / anion exchanger URAT1. For this reason, they have five to ten times higher uric acid levels in serum than other mammals.

A - only animals in question - the vast waste nitrogen excretion on uric acid is called Uricotelie.

In the marine polychaete Platynereis dumerilii uric acid acts as a pheromone, which is emitted by the females during mating of the animals into the water. There it releases the sperm release from the male.

Physicochemistry

Uric acid has different manifestations at, reduced and oxidized. Consequently, it depends on the environment around the uric acid, which redox state. After that also decides whether and how long received with a reactant a bond.

Pathophysiology

Under certain conditions, it may come in the organism to increased production of uric acid. The most common reason is insufficient excretion of uric acid by the kidneys. If the solubility product is exceeded it, the uric acid can precipitate in the urinary tract, in the blood stream and in bradytrophic tissues and are deposited.

Consequence of this hyperuricemia can uroliths ( urinary stones ), his gout and uric acid infarcts. The sodium salt of uric acid, sodium urate, plays an essential role because it settles then as crystals (gout) or stones (kidney stones).

Certain factors increase the production of uric acid or the amount of uric acid in the body:

  • Diseases haemoblastoses
  • Glycogen storage diseases
  • Lesch -Nyhan syndrome
  • Idiopathic hypercalcemia
  • Hypertriglyceridemia
  • Chronic kidney failure (renal failure)
  • Acute tumor lysis syndrome
  • Medication (eg, thiazide diuretics, loop diuretics)
  • Radiotherapy

The determination of uric acid concentration in tumor therapy with cytotoxic drugs or ionizing radiation is of great importance. If larger tumor and cell mass is destroyed, the uric acid content in the blood rises quickly, so that it can lead to serious kidney damage. Through regular monitoring tumor therapy must be controlled so that critical uric acid levels are not reached.

Ethanol inhibits the excretion of uric acid.

In a large epidemiological study elevated uric acid levels were in the normal population, a moderate risk factor of developing chronic kidney disease in the further course.

Metabolic Syndrome

The founder of Giovanni Battista Morgagni Pathology (1682-1771; professor in Padua ) recognized in the 18th century, the relationship between obesity, diabetes mellitus, hypertension and gout. In the " first description " of the metabolic syndrome ( MetS ) by the Swedes E. Kylin 1923 addition to the increase of body weight, blood fats and blood sugar still hyperuricemia is mentioned. In the definitions currently valid example the International Diabetes Foundation (IDF ) is missing the hyperuricemia. An increasing number of scientists it takes but again in their definition of MetS.

Detection reactions

The uric acid content can be measured by photometry using the urate oxidase and an absorption in the range of 290 nm in the enzyme assay.

Another common test is based on the evaporation of uric acid with concentrated nitric acid and addition of ammonia solution in the murexide sample.

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