Which enzyme catalyzes the rate-limiting step in the synthesis of catecholamines from tyrosine?
- A Tyrosinase
- B Dopa decarboxylase
- C Tyrosine hydroxylase ✓
- D Phenylethanolamine N-methyltransferase
Correct answer: C. Tyrosine hydroxylase
Explanation
Tyrosine hydroxylase converts tyrosine to L-DOPA using tetrahydrobiopterin as cofactor, and it is the rate-limiting enzyme of catecholamine synthesis, subject to feedback inhibition by catecholamines. Tyrosinase performs the first step of melanin synthesis, dopa decarboxylase forms dopamine, and PNMT converts norepinephrine to epinephrine in the adrenal medulla under cortisol influence; none of these limits overall flux.
Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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