Once in the cytosol, sialic acids are either reutilized or degraded. N-acetylneuraminate lyase (NPL) is a cytosolic, tetrameric enzyme that can cleave the major sialic acids N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) to form N-acetylmannosamine (ManNAc) and N-glycolylmannosamine (ManNGc) respectively (Wu et al. 2005). Although humans cannot form Neu5Gc due to a non-functional CMAHP enzyme, Neu5Gc can be ingested by dietary means and must therefore be degraded to avoid accumulation of this immunoreactive sialic acid (Bergfeld et al. 2012).
N-acetylneuraminate lyase activity of NPL tetramer [cytosol]