TSTA3 dimer reduces GDP-KDGal to GDP-Fuc

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 second stage, 4-reductase activity of TSTA3 dimer catalyses a hydride transfer from NADPH to the keto group at C-4 of GDP-4-keto-6-deoxygalactose (GDP-KDGal), yielding GDP-fucose (GDP-Fuc) and NADP+.

GDP-L-岩藻糖的从头合成途径为一个始于GDP-甘露糖的两步反应路径。在第二步中，GDP-4-脱氢-6-去氧-α-D-甘露糖（GDP-DHDMan）发生异头异构化并还原为GDP-L-岩藻糖（GDP-Fuc）。细胞质中的酶GDP-L-岩藻糖合酶（TSTA3，亦称FX）似乎具有异头异构酶和还原酶的活性，并作为同源二聚体（Tonetti 等人，1996年，Zhou 等人，2013年）发挥作用。在第二阶段，TSTA3二聚体的4-还原酶活性催化NADPH中的氢转移至GDP-4-酮-6-去氧半乳糖（GDP-KDGal）的C-4位的酮基，生成GDP-岩藻糖（GDP-Fuc）和NADP+。