Fig. 3.

The one carbon cycle. Importance of group B vitamins and Zinc in Homocysteine recycling. Homocysteine can be recycled using three pathways; however the only one strongly expressed in the human oocyte is the MS pathway. The betaine-dimethyl glycine pathway is weakly expressed and the CBS pathway is totally absent during the pre-genomic activation period. SAH S-Adenosyl Homocysteine; SAM S-Adenosyl Methionine; THF tetrahydrofolate, CBS cystathionine beta synthase; MS Methionine synthase; MTHFR Methyltetrahydrofolate reductase Zn Zinc