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, N-acylglucosamine 2-epimerase (RENBP) dimer catalyses the reversible isomerisation of N-acetylmannosamine (ManNAc) to N-acetylglucosamine (GlcNAc) and of N-glycolylymannosamine (ManNGc) to N-glycolylglucosamine (GlcNGc) (Takahashi et al. 1999, 2001).
N-acylglucosamine 2-epimerase activity of RENBP dimer [cytosol]