## **Core Concept**
The question tests knowledge of the intermediate products in amino acid metabolism, specifically focusing on the metabolism of histidine. FIGLU (Formiminoglutamate) is a key intermediate in this pathway.

## **Why the Correct Answer is Right**
The correct answer, **Histidine**, is metabolized through a series of steps, one of which involves the conversion of formiminoglutamate (FIGLU) to glutamate. FIGLU is formed from the breakdown of histidine by the action of histidase, which converts histidine into urocanate, then through further reactions, urocanate is converted into FIGLU. This process is crucial in the catabolism of histidine.

## **Why Each Wrong Option is Incorrect**
- **Option A: Tyrosine** - Tyrosine metabolism primarily involves its conversion into acetoacetate and fumarate through the tyrosine degradation pathway, which does not produce FIGLU as an intermediate.
- **Option B: Tryptophan** - Tryptophan is metabolized through the kynurenine pathway, leading to the production of niacin or through other pathways to alanine and acetoacetyl-CoA, not involving FIGLU directly.
- **Option D: Arginine** - Arginine metabolism is closely related to the urea cycle, where arginine is converted into urea and ornithine. This pathway does not involve FIGLU.

## **Clinical Pearl / High-Yield Fact**
A clinical pearl related to FIGLU is its association with folate deficiency. Elevated levels of FIGLU in urine can be an indicator of folate deficiency because FIGLU requires tetrahydrofolate (THF) for its further metabolism to glutamate. In folate deficiency, this conversion is impaired, leading to increased excretion of FIGLU.

## **Correct Answer:** C. Histidine