Creatine biosynthesis begins with transfer of the amidino group of arginine to glycine, forming guanidinoacetate. The final methylating step converts guanidinoacetate to creatine using S-adenosylmethionine. Which organ performs this terminal methylation?
- A Kidney only
- B Liver ✓
- C Skeletal muscle
- D Brain
Correct answer: B. Liver
Explanation
Guanidinoacetate formed by arginine:glycine amidinotransferase in the kidney travels to the liver, where guanidinoacetate N-methyltransferase adds a methyl group from S-adenosylmethionine to yield creatine. Creatine then reaches muscle and brain via blood for phosphorylation to phosphocreatine. Muscle takes up creatine but does not synthesize it de novo, and neither brain nor kidney expresses significant guanidinoacetate methyltransferase activity.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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