Glucosamine metabolism in Drosophila virilis salivary glands: Ontogenetic changes of enzyme activities and metabolite synthesis

In Drosophila virilis salivary glands the in vitro activities of enzymes involved in the glucosamine pathway were examined during the third larval instar and in the prepupa. While glutamine-fructose-6-phosphate aminotransferase (EC 5.3.1.19) becomes inactive at the time of puparium formation, glucosamine-6-phosphate isomerase (EC 5.3.1.10) and glucosamine-6-phosphate N-acetyltransferase (EC 2.3.1.3) show maximal activities in the prepupal gland. The activity of UDP-N-acetylglucosamine pyrophosphorylase (EC 2.7.7.23) may also decrease prior to puparium formation. Incubation of larval and prepupal glands in medium containing ³H]glucose + ¹⁴C]-uridine or ¹⁴C]glucosamine and subsequent separation of intermediates of the glucosamine pathway by chromatographic procedures reveal that the capacity of the glands to incorporate the isotopes into these intermediates decreases significantly at the time of puparium formation. The results suggest that in D. virilis salivary glands the formation of aminosugars is mainly controlled by the activities of the two enzymes glutamine-fructose-6-phosphate aminotransferase and UDP-N-acetylglucosamine pyrophosphorylase.