Nascent glycoproteins with a chitin-like carbohydrate component in Drosophila melanogaster imaginal discs

The incorporation of 1-³H]d-glucosamine in Drosophila melanogaster imaginal discs revealed the synthesis of glycoproteins represented by a family of subfractions with roughly the same molecular mass of about 80,000 and discrete isoelectric point values in the range of 5.0 to 6.5 pH units. The incorporation of 1-³H]d-glucosamine was not inhibited by tunicamycin, an inhibitor of N-glycosylation. This family of glycoproteins is relatively protease-resistant but can be digested by high concentrations of pronase E (100 μg/ml) or pepsin (1 mg/ml). The carbohydrate component of these glycoproteins is sensitive to chitinase. The properties of the glycoproteins in imaginal discs are similar to those of chitinase sensitive glycoproteins found in established cell cultures of D. melanogaster Kramerov et al., Insect Biochem. 16, 417–432 (1986)]. Incorporation of 1-³H]d-glucosamine into the family of glycoproteins decreases as the imaginal discs undergo evagination induced by 20-hydroxyecdysone.