5-Methyltetrahydrofolate (5-Me-THF)

5-Methyltetrahydrofolate, the predominant metabolic form of folate, is a methylated derivate of tetrahydrofolate. It is generated by methylenetetrahydrofolate reductase (MTHFR) from 5,10-methylenetetrahydrofolate and used to recycle homocysteine back to methionine by 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR) or methionine synthase (MS). Levomefolic acid (INN) or metafolin is the natural, active form of folic acid used at the cellular level for DNA reproduction, the cysteine cycle and the regulation of homocysteine among other functions. The un-methylated form, folic acid (vitamin B₉), is a synthetic form of folate found in nutritional supplements. Synthetic folic acid is metabolized in the body into levomefolic acid. Approximately 10% of the general population (homozygous TT) lack the enzymes needed to receive any benefit from folic acid.