in the "trans"-golgi a glcnac phosphotransferase (ec 2.7.8.17) adds a glcnac-1-phosphate residue onto the 6-hydroxyl group of a specific mannose residue within the oligosaccharide. this forms a phosphodiester: man-phosphate-glcnac. once the phosphodiester has been formed the lysosomal enzyme will be translocated through the golgi apparatus to the "trans"-golgi. in the "trans"-golgi a phosphodiesterase (ec 3.1.4.45) will remove the glcnac residue exposing the mannose 6-phosphate tag, allowing the lysosomal enzymes to bind to the ci-mpr and the cd-mpr. the mpr-lysosomal enzyme complex is translocated to a pre-lysosomal compartment, known as an endosome, in a clathrin-coated vesicle. this targeting away from the secretory pathway is achieved by the presence of a specific sorting signal, an acidic cluster/dileucine motif, in the cytoplasmic tails of the mprs. both mprs bind their ligands most effectively at ph 6 – 7; thus enabling the receptors to bind to the lysosomal enzymes in the "trans"-golgi and release them in the acidified environment of the endosome. once the enzyme has dissociated from the mannose 6-phosphate receptor, it is translocated from the endosome to the lysosome where the phosphate tag is removed from the enzyme.