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Stepwise modification of N-linked carbohydrate chain on lysosomal hydrolases in the Golgi

Starting at the lower left of the illustration, in the cis-Golgi network, GlcNAc-1-phosphotransferase phosphorylates selected mannose residues on lysosomal enzymes. In the process uridine diphosphate (UDP) is converted to uridine monophosphate (UMP). Then, N-acetylglucosamine (GlcNAc) is removed by the uncovering enzyme (UCE) in the trans-Golgi network (Rohrer J, Kornfeld R. Lysosomal hydrolase mannose 6-phosphate uncovering enzyme resides in the trans-Golgi network. Mol Biol Cell 2001;12(6):1623-31.)

The phosphorylated enzymes bind with the mannose 6-phosphate (M6P) receptor and are internalized to the endosome and finally enter the lysosomes. (Source: Khan SA, Tomatsu SC. Mucolipidoses overview: past, present, and future. Int J Mol Sci 2020;21(18):6812. Enlarged and edited by Douglas J Lanska MD MS MSPH to improve sharpness and contrast. Creative Commons Attribution [CC BY] license. http://creativecommons.org/licenses/by/4.0.)