A patient with megaloblastic anemia undergoes a histidine load test. Within hours, large amounts of formiminoglutamic acid (FIGLU) appear in the urine. This accumulation occurs because FIGLU cannot be converted to glutamate without which cofactor?
- A Tetrahydrobiopterin
- B Pyridoxal phosphate
- C Tetrahydrofolate ✓
- D Thiamine pyrophosphate
Correct answer: C. Tetrahydrofolate
Explanation
In histidine catabolism, formiminoglutamic acid transfers its formimino group to tetrahydrofolate, yielding glutamate and N5-formimino-THF. Folate deficiency blocks this step, so FIGLU accumulates and is excreted, forming the basis of the FIGLU excretion test. Pyridoxal phosphate serves many transamination reactions but is not the acceptor for the formimino group, eliminating option B.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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