The exchange of sulfur, or sulfur-containing moiety, between two different compounds.
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6] is widely recognized for its importance in the inactivation of homocysteine by serving as coenzyme in the form of PLP for two degradative enzymes (cystathionine [beta]-synthase and cystathionine [gamma]-lyase) in the transsulfuration pathway for homocysteine removal (Selhub, 1999; Miles and Kraus, 2004).
Is the increase in serum cystathionine levels in patients with liver cirrhosis a consequence of impaired homocysteine transsulfuration at the level of gamma-cystathionase?
Alternatively, homocysteine can be directed to the transsulfuration pathway and used in the synthesis of GSH (Figure 1).
Homocysteine can be regenerated to methionine via the remethylation pathway or irreversibly degraded to cysteine via transsulfuration.
SAH then is broken down by SAH hydrolase (SAHH) to form homocysteine, which can either enter a set of reactions called the transsulfuration pathway to form glutathione (GSH) or be remethylated to form methionine (Grillo and Colombatto 2008).
Firstly, Hcy react with serine to form Ctn by catalytic action of cystathionine [beta]-synthase (CBS) through the transsulfuration pathway.
According to the transsulfuration data, it can be concluded that the higher cystine formation with HMTBA compared to DLM could explain the higher glutathione level observed in the present study.
Both pathways require vitamin-derived cofactors, pyridoxine for transsulfuration and both folate and cobalamin in the methionine cycle.
Hcy metabolized through the transsulfuration and transmethylation pathways, where folate, vitamin B-12 and vitamin B-6 are involved as a substrate or cofactor.
There are two pathways for the metabolism of homocysteine: 1) vitamin B6 dependent transsulfuration, which leads to formation of cysteine irreversibly, 2) folate and vitamin B12 dependent remethylation to form methionine by help of methionine synthase.