The de novo synthesis pathway for GDP-L-fucose is a two step pathway starting from GDP-mannose. In the second step, GDP-4-dehydro-6-deoxy-alpha-D-mannose (GDP-DHDMan) is epimerised and reduced to GDP-L-fucose (GDP-Fuc). The cytosolic enzyme GDP-L-fucose synthase (TSTA3, aka FX) appears to have both epimerase and reductase activities and functions as a homodimer (Tonetti et al. 1996, Zhou et al. 2013). In the first stage, the hydroxyl group at C-3 and the methyl group at C-5 of the mannose ring of GDP-DHDMan are epimerised to GDP-4-keto-6-deoxygalactose (GDP-KDGal).
Yu, F, Liu, Y, Xu, C, Sun, L, Ji, C, He, J, Li, J, Zhou, H
Bisso, A, De Flora, A, Benatti, U, Tonetti, M, Sturla, L
isomerase activity of TSTA3 dimer [cytosol]
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