Lysosomal-enzyme targeting: the phosphorylation of synthetic D-mannosyl saccharides by UDP-N-acetyl-glucosamine:lysosomal-enzyme N-acetylglucosamine-phosphotransferase from rat-liver microsomes and fibroblasts.
Phosphorylation of the D-mannose residues of lysosomal enzymes is essential for the uptake and intracellular transport of these enzymes to lysosomes. The GlcNAc-P-transferase which is involved in the phosphorylation reaction seems to recognize a signal, probably a protein conformation, common to many lysosomal enzymes. To evaluate the role of the carbohydrate portion of the enzyme in these phosphorylation reactions, the acceptor specificity of GlcNAc-P-transferase from rat-liver microsomes and fibroblasts was examined with the aid of synthetic D-mannosyl disaccharides and derivatives that are closely related to the high-mannose type of oligosaccharides. Four methyl D-mannobiosides were synthesized, and their structures were established by 13C-n.m.r. spectroscopy. Of all the D-mannosyl saccharides tested, alpha-D-Man-(1----2)-alpha-D-Man-(1----OMe) was found to be the best acceptor, thereby suggesting that oligosaccharide structure may also have a role to play in recognition by this enzyme.
D000818:Animals; D005347:Fibroblasts / Q000201:enzymology; D007202:Indicators and Reagents; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008351:Mannans / Q000138:chemical synthesis*; D008862:Microsomes, Liver / Q000201:enzymology*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism*; D051381:Rats; D013379:Substrate Specificity; D017855:Transferases (Other Substituted Phosphate Groups)
D007202:Indicators and Reagents; D008351:Mannans; D010770:Phosphotransferases; D017855:Transferases (Other Substituted Phosphate Groups); C030012:UDP-N-acetylglucosamine-lysosomal-enzyme-N-acetylglucosaminephosphotransferase