Transsulfuration pathway

The transsulfuration pathway is a metabolic pathway that converts cysteine to homocysteine, through the intermediate cystathionine. This pathway can have many different functions. In organisms that synthesise cysteine in sulfur assimilation, the production of homocysteine through transsulfuration allows the conversion of this intermediate to methionine, through a methylation reaction carried out by methionine synthase. In other organisms, transsulfuration works in the opposite direction and is involved in breaking down excess methionine.