Métabolisme du tréhalose et du glycogène chez le Ver à soie, en relation avec la mue, le filage et les métamorphoses

Abstract

In the silkworm, as is the case in most other insects, trehalose is the principal circulating form of the saccharidic cellular food. The hemolymph contains an enzyme, trehalase, which is normally inhibited. The inhibition is only suppressed during the periods of molting, causing a decrease of the trehalose concentration and an increase of the amount of free glucose. The muscles and most other tissues, such as the digestive tract, are able to use blood trehalose, thanks to an intracellular trehalase. The epidermis and the silk-glands are devoid of trehalase : they use the free glucose liberated by the hydrolysis of the hemolymph trehalose during the periods of molting and spinning. The problem of the origin of the trehalose is discussed, in the light of recent experiments, in which the incorporation of radioactivity from labelled pyruvate and glucose-1-phosphate into fat-body glycogen and hemolymph trehalose has been followed. The chitin of the cuticle is synthesized at every molting process, partly at the expense of the glucose liberated by the hydrolysis of the trehalose in the hemolymph. On the other hand, the old cuticle is destroyed by the proteolytic and chitinolytic enzymes of the exuvial fluid. The hydrolytic products, especially N-acetylglucosamine, are resorbed by the epidermis and can be used for the biosynthesis of the chitin of the new cuticle.