SYN: vitamin B12.
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meth·yl·co·bal·a·min (meth″əl-ko-balґə-min) a cobalamin derivative in which the substituent is a methyl group. It is one of two metabolically active forms synthesized upon ingestion of vitamin B12 and is the predominant form in the serum; it acts as a coenzyme in the reaction catalyzed by 5-methyltetrahydrofolate-homocysteine methyltransferase. Abbreviated MeCbl.Medical dictionary. 2011.