Question:
Conversion of norepinephrine to epinephrine is mainly by which of the following?
Conversion of norepinephrine to epinephrine is mainly by which of the following?
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SAM is the methyl donor for PNMT converting NE to epinephrine.
Updated On: Jun 23, 2026
- S-adenosyl methionine
- Arginine
- Phenylalanine
- Dehydrogenase
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The Correct Option is A
Solution and Explanation
Step 1: The final step of catecholamine synthesis is the methylation of norepinephrine to form epinephrine.
Step 2: This reaction is catalyzed by the enzyme phenylethanolamine N-methyltransferase (PNMT).
Step 3: PNMT requires a methyl donor, and that donor is S-adenosyl methionine (SAM). SAM donates the methyl group for the conversion of norepinephrine to epinephrine, so option a is correct.
Step 4: Arginine (b) is a precursor for nitric oxide and the urea cycle, phenylalanine (c) is an upstream amino acid precursor of tyrosine but not the methyl donor for this step, and a dehydrogenase (d) catalyzes oxidation-reduction, not methylation. Hence S-adenosyl methionine is the answer.
Step 2: This reaction is catalyzed by the enzyme phenylethanolamine N-methyltransferase (PNMT).
Step 3: PNMT requires a methyl donor, and that donor is S-adenosyl methionine (SAM). SAM donates the methyl group for the conversion of norepinephrine to epinephrine, so option a is correct.
Step 4: Arginine (b) is a precursor for nitric oxide and the urea cycle, phenylalanine (c) is an upstream amino acid precursor of tyrosine but not the methyl donor for this step, and a dehydrogenase (d) catalyzes oxidation-reduction, not methylation. Hence S-adenosyl methionine is the answer.
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