It is no surprise that the C1-metabolism in all its complexity involves more than one vitamin. The step from THF to N‑5,10-methylene‑THF is pyridoxine (vitamin B6)-dependent. The step from N‑5,10-methylene‑THF to N‑5-methyl-THF needs riboflavin (vitamin B2). The step from N‑5-methyl-THF to THF that transfers a methyl-group from homocysteine to methionine is vitamin B12 (cobalamin)-dependent. The conversion from homocysteine to cysteine has two steps that are both pyridoxine (vitamin B6)-dependent (Škovierová et al., 2016).