histidine catabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways resulting in the breakdown of histidine, 2-amino-3-(1H-imidazol-4-yl)propanoic acid. [GOC:go_curators]

Histidine catabolism is the process by which the amino acid histidine is broken down in living organisms. It is a complex pathway involving multiple enzymes and reactions, ultimately leading to the production of ammonia, carbon dioxide, and energy.

**Step 1: Deamination**
Histidine is initially deaminated by the enzyme histidase, producing urocanic acid. This reaction releases ammonia, which is a waste product that needs to be excreted from the body.

**Step 2: Hydration**
Urocanic acid is then hydrated by the enzyme urocanase, forming N-formiminoglutamate (FIGLU).

**Step 3: Tetrahydrofolate-dependent Transfer**
FIGLU is subsequently converted to glutamate by the enzyme formiminotransferase, which requires tetrahydrofolate (THF) as a cofactor. This step involves the transfer of a formimino group (CHNH) from FIGLU to THF, producing N5-formimino-THF.

**Step 4: Formimino-THF Breakdown**
N5-formimino-THF is then converted to N10-formyl-THF by the enzyme formimino-THF cyclodeaminase. This reaction releases ammonia and carbon dioxide.

**Step 5: Glutamate Metabolism**
The glutamate produced in step 3 can enter the citric acid cycle, where it is further oxidized to generate energy.

**Regulation**
The histidine catabolic pathway is tightly regulated to ensure proper balance of histidine and its breakdown products. The activity of histidase, the first enzyme in the pathway, is regulated by feedback inhibition from urocanic acid. Additionally, the availability of THF, a cofactor for formiminotransferase, can influence the rate of histidine catabolism.

**Clinical Significance**
Deficiencies in enzymes involved in histidine catabolism can lead to various genetic disorders, including histidinemia and formiminotransferase deficiency. These disorders can cause neurological problems, developmental delays, and other health issues.

Histidine catabolism is essential for maintaining nitrogen balance, providing energy, and supporting various metabolic processes. It is a complex and highly regulated pathway that plays a crucial role in human health.'
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Proteins (2)

Compounds (5)