Fig. 2
From: Genetic approaches to understanding the causes of stuttering
Two-steps adding mannose-6-phosphate markers on lysosomal enzymes. In the first step, GlcNAc-phosphotransferase (GNPTAB/G) transfer GlcNAc-1-phosphate from UDP-GlcNAc to terminal mannose residues of N-linked glycans on enzymes destined to the lysosome. In the second step, N-acetylglucosamine-1-phosphodiester-alpha-N-acetylglucosaminidase (NAGPA), also known as the uncovering enzyme, cleaves off the GlcNAc residue, thereby exposing mannose-6-phosphate (circled). Enzymes with this recognition marker are then transported from Golgi to the lysosome