Although F9 cells labelled with [3H]glucosamine synthesize many glycoproteins that bind to Datura stramonium agglutinin-agarose, only a small proportion of these were immunoprecipitated with monoclonal antibodies to lamp-1 and lamp-2 (lamp = lysosomal membrane protein). Differentiation of F9 cells by retinoic acid increased labelling of all Datura stramonium-bound glycoproteins, including lamp-1 and lamp-2. Although the large polylactosaminoglycans excluded from Bio-Gel P-6 that are characteristic of F9 cells were obtained from total glycoproteins, little of these large polylactosaminoglycans was found on lamp-1 and lamp-2. There was no increase in large polylactosaminoglycans of lamp-1 and lamp-2 after retinoic acid treatment, but an increase in the size of small polylactosaminoglycans (included on Bio-Gel P-6) and tri- and tetra-antennary complex oligosaccharides. Therefore, other factors besides the expression of specific glycosyltransferases determine the extent of elongation of polylactosaminoglycans on lysosomal membrane proteins.
Functional characterization of the lysosomal membrane protein TMEM192 in mice