A patient with megaloblastic anemia excretes large amounts of formiminoglutamic acid (FIGLU) in urine after a histidine load. This occurs because FIGLU, an intermediate of histidine catabolism, normally requires which cofactor for conversion to glutamic acid?
- A Tetrahydrofolate ✓
- B Pyridoxal phosphate
- C Tetrahydrobiopterin
- D Thiamine pyrophosphate
Correct answer: A. Tetrahydrofolate
Explanation
In histidine degradation, formiminoglutamate receives a formimino group transfer requiring tetrahydrofolate, yielding glutamate and N5-formimino-THF. When folate is deficient, FIGLU accumulates and spills into urine, which forms the basis of the historical FIGLU excretion test for folate deficiency. Pyridoxal phosphate serves transamination and decarboxylation reactions, tetrahydrobiopterin serves hydroxylases, and thiamine pyrophosphate serves alpha-ketoacid decarboxylation, none of which participate here.
Reference: Lippincott Illustrated Reviews: Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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