Homocystein - Metabolismus
Figure 1: Pathways of homocysteine metabolism (CBS = cystathionine-beta-synthase; Cbl = cobalamin; THF1 = monoglutamated form of tetrahydrofolate; B6 = vitamin B6; CH3 = Methyl). Homocysteine is metabolized either by transsulfuration to cysteine
(in a reaction catalyzed by cystathionine-beta-synthase [(CBS] with vitamin B6 as cofactor) or by remethylation to methionine. Remethylation
is catalyzed by methionine synthase (and 5,10 methylenetetrahydrofolate reductase). Methionine synthase is dependent upon cobalamin (vitamin B12) as cofactor and folate as cosubstrate. An alternative remethylation pathway (not shown in the figure) uses the cobalamin independent betain-homocysteine methyltransferase.