NPL cleaves Neu5Ac,Neu5Gc to ManNAc,ManNGc and pyruvate

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).

一旦进入细胞质，唾液酸要么被再利用，要么被降解。N-乙酰神经氨酸酯酶（NPL）是一种细胞质中的四聚体酶，能够将主要的唾液酸N-乙酰神经氨酸（Neu5Ac）和N-甘露酰神经氨酸（Neu5Gc）分别裂解，形成N-乙酰甘露糖胺（ManNAc）和N-甘露酰甘露糖胺（ManNGc）（Wu等，2005年）。由于人类无法形成Neu5Gc，这是由于CMAHP酶的非功能性所致，因此Neu5Gc可以通过饮食途径摄入，因此必须降解以避免这种免疫反应性唾液酸的积累（Bergfeld等，2012年）。