Amino Sugar Metabolism in the Silkworm, Bombyx mori

抄録

1. D-Glucosamine-1-¹⁴C, N-acetyl-D-glucosamine-1-¹⁴C, D-glucosaminic acid-1-¹⁴C, and D-glucose-1-¹⁴C were administered to larvae of the silkworm, and the amounts of the isotope in expired CO₂ and silk proteins were determined.
2. After 4 hours, CO₂ exhaled from feeding larvae contained 14.5, 8.7, 2.5, and 1.5% of isotope injected as glucose, glucosaminic acid, glucosamine, and N-acetylglucosamine, respectively. In spinning larvae, considerable changes were observed in the rate of oxidation of these amino sugars.
3. Fibroin and sericin were isolated from cocoons and hydrolyzed to determine the specific activities of amino acids, hexosamines, and hexoses. All the compounds investigated were efficiently incorporated into silk proteins not only as hexosamines and hexoses, but also as serine, alanine, glycine, aspartic, and glutamic acids. No radioactivity was associated with other amino acids. The labeling patterns obtained with glucosamine and N-acetylglucosamine were similar to that with glucose, suggesting that these sugars were mainly metabolized by the same pathway. Experiments with glucosaminic acid revealed a considerable difference in the relative distribution of isotope among amino acids, suggesting that the catabolism of this compound is different from that of glucose.
4. These results indicate that hexosamine metabolism in the silkworm differs markedly from that in mammals and microorganisms.