NAGK dimer phosphorylates GlcNAc, GlcNGc to GlcNAc-6-P, GlcNGc-6-P

Humans are not able to catalyse the formation of N-glycolylneuraminic acid (Neu5Gc) due to an inactive CMAHP enzyme. Neu5Gc can be obtained from dietary sources and must be degraded to avoid accummulation and resultant chronic inflammation known as xenosialitis (Varki et al. 2011). Degradation of excess Neu5Gc results in the formation of two ubiquitous metabolites involved in asparagine N-linked glycosylation; glycolate and glucosamine 6-phosphate. In the Neu5Gc degradation pathway, a salvage reaction of amino sugar metabolism utilises dimeric GlcNAc kinase (NAGK) to phosphorylate N-acetylglucosamine (GlcNAc) to GlcNAc-6-phosphate and N-glycolylglucosamine (GlcNGc) to GlcNGc-6-P (Hinderlich et al. 2000, Weihofen et al. 2006).

人类因CMAHP酶活性不足，无法催化N-糖基神经氨酸酸（Neu5Gc）的生成。Neu5Gc可通过膳食来源摄取，但需降解以避免积累，进而引发异源性神经酸脂炎（xenosialitis），该炎症为慢性炎症之一（Varki et al. 2011）。过量的Neu5Gc降解将产生两种普遍存在的代谢物，它们参与天冬酰胺N-连接糖基化；分别为甘醇酸和葡萄糖胺-6-磷酸。在Neu5Gc降解途径中，氨基酸糖代谢的挽救反应利用二聚体甘露糖-6-磷酸化酶（NAGK）将N-乙酰葡萄糖胺（GlcNAc）磷酸化为甘露糖-6-磷酸和N-糖基葡萄糖胺（GlcNGc），最终转化为甘露糖-6-磷酸（GlcNGc-6-P）（Hinderlich et al. 2000, Weihofen et al. 2006）。