Most one‑carbon transfers are promoted by one of three cofactors: biotin, tetrahydrofolate, or s‑adenosylmethionine. s‑adenosylmethionine is generally used as a methyl group donor; the transfer potential of the methyl group in n 5 ‑methyltetrahydrofolate is insufficient for most biosynthetic reactions. however, one example of the use of n 5 ‑methyltetrahydrofolate in methyl group transfer is in methionine formation by the methionine synthase reaction; methionine is the immediate precursor of s‑adenosylmethionine. list the three methyl donors in order of methyl group transfer potential highest to lowest.