Chitin Degradation

Degradation of chitin is physiologically crucial for normal growth and development of insects. Chitin is degraded by the joint action of chitinase, which yields oligomeric fragments, and exochitinase, or P-A-acetylglucosaminidase, which hydro lyzes terminal polymers or dimers. These hydrolytic enzymes are widespread in plants, vertebrates, invertebrates, and microorganisms. During the complex molting process in arthropods, the chitin in the cuticular region (the endocuticle), which is close to the epidermal cells, is degraded. Since chitin microfibrils are tightly associated with various cuticular proteins, proteolytic activity accompanies and facilitates chitin hydrolysis. Hydrolysis of chitin does not occur in the exocuticle, where sclerotization of the cuticular protein takes place. Formation and secretion of chitinases by epidermal cells, processes that are under hormonal control, are vital for the molting process. The mono- and disaccharide degradation products are absorbed by the epithelial cells and may be recycled to serve for biosynthesis of the new chitin.

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