Hcy, (2S)-2-amino-4-sulfanylbutanoic acid

Homocysteine is a cysteine homologue and synthesized from and to methionine in a pyridoxine (vitamin B6)-, cobalamin- (vitamin B12)- and riboflavin (vitamin B2)-dependent circulatory system. The core of the cascade is the transmethylation of methionine that can lead to synthesis of cysteine. The reverse reactions from homocysteine to methionine involve two paths that are either folate/B12/B2 or choline/betaine dependent (Škovierová et al., 2016).

Hyperhomocysteinaemia and homocystinuria have been associated with many cardiovascular and age-related pathologies and cancers that have received attention (Kumar et al., 2017, Škovierová et al., 2016). During pregnancy high homocysteine concentrations cause neural tube defects, preeclampsia, placental disruption, intrauterine growth retardation, low birth weight and increase the risk for recurrent early pregnancy loss (McNulty et al., 2019). These can be countered through folate and cobalamin (vitamin B12) supplementation (McNulty et al., 2019)

Image from (PubChem, 2020a): L-homocysteine
Image from (PubChem, 2020): L-homocysteine; https://pubchem.ncbi.nlm.nih.gov/compound/L-Homocysteine