Formiminoglutamic acid

Formiminoglutamic acid (FIGLU) is a metabolite of the amino acid histidine. It is formed during the metabolism of histidine in a process that involves the enzyme histidase. Formiminoglutamic acid is an important compound in the study of folate metabolism and homocysteine levels, as its excretion in urine can be an indicator of folate deficiency or malfunction in folate-related metabolic pathways.

Metabolism

Formiminoglutamic acid is produced in the liver from histidine through the action of histidase. This reaction is part of the histidine degradation pathway, which converts histidine into ammonia and urocanic acid, with formiminoglutamic acid being an intermediate. The metabolism of FIGLU is heavily dependent on the availability of folate, as it requires a folate-dependent enzyme, formiminotransferase cyclodeaminase, to convert it into glutamic acid. This conversion is crucial for the entry of FIGLU into the citric acid cycle, where it can be used for energy production or for the synthesis of other compounds.

Clinical Significance

The measurement of formiminoglutamic acid levels in urine after a histidine load can be used as a diagnostic test for folate deficiency. Elevated levels of FIGLU in the urine indicate that folate metabolism is impaired, as folate is necessary for the conversion of FIGLU to glutamic acid. This test, known as the FIGLU excretion test, was historically used before more direct methods of measuring folate levels became available.

In addition to its role in diagnosing folate deficiency, elevated FIGLU levels have been investigated for their potential association with increased risk of cardiovascular diseases due to elevated homocysteine levels. Homocysteine is another metabolite involved in folate metabolism, and its levels can be indicative of cardiovascular risk.

See Also

• Folate
• Homocysteine
• Histidine metabolism
• Citric acid cycle

References

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