Chitin is one of the most important biopolymers in nature. It is mainly produced by fungi, arthropods and nematodes. In insects, it functions as scaffold material, supporting the cuticles of the epidermis and trachea as well as the peritrophic matrices lining the gut epithelium. Insect growth and morphogenesis are strictly dependent on the capability to remodel chitin-containing structures. For this purpose, insects repeatedly produce chitin synthases and chitinolytic enzymes in different tissues. Coordination of chitin synthesis and its degradation requires strict control of the participating enzymes during development. In this review, we will summarize recent advances in understanding chitin synthesis and its degradation in insects.

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Chitin metabolism in insects: structure, function and regulation of chitin synthases and chitinases

Reserve polysaccharides are formed by plant cells at certain physiological stages of development, usually during periods of intense photosynthetic activity, and are later “digested” to deliver carbohydrate monomers which re-enter the cells’ metabolism. They are stored — that is temporarily withdrawn from cellular metabolism — either in the solid state or, less frequently, in a dissolved or highly hydrated colloidal state. Their deposition takes place on the outside of the plasmalemma in the cell wall region, in plastids or in cell vacuoles. As far as we know, starch is the only polysaccharide formed in plastids and the plastids constitute the only cellular compartment which forms starch in higher plants.

Reserve Polysaccharides Other Than Starch in Higher Plants

Three proteins which display chitinase activity were purified from the supernatants of Trichoderma harzianum CECT 2413 grown in minimal medium supplemented with chitin as the sole carbon source. Purification was carried out after protein precipitation with ammonium sulphate, adsorption to colloidal chitin and digestion, and, finally, chromatofocusing. By this procedure, two chitinases of 42 kDa (CHIT42) and 37 kDa (CHIT37) were purified to homogeneity, as judged by SDS/PAGE and gel filtration, whereas a third, of 33 kDa (CHIT33), was highly purified. The isoelectric points for CHIT42, CHIT37 and CHIT33 were 6.2, 4.6 and 7.8, respectively. The three enzymes displayed endochitinase activities and showed different kinetic properties. CHIT33 was able to hydrolyze chitin oligomers of a polymerization degree higher than n= 4, its Km for colloidal chitin being 0.3 mg/ml. CHIT42 and CHIT37 were able to hydrolyze chitin oligomers with a minimal polymerization degree of n= 3, their Km values for colloidal chitin being 1.0 mg/ml and 0.5 mg/ml respectively. With regard to their lytic activity with purified cell walls of the phytopathogenic fungus Botrytis cinerea, a hydrolytic action was observed only when CHIT42 was present. Antibodies against CHIT42 and CHIT37 specifically recognized the proteins and did not display cross-reaction, suggesting that each protein is encoded by a different gene.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1992.tb16994.x

Isolation and characterization of three chitinases from Trichoderma harzianum.

Insect chitin: Physical state, synthesis, degradation and metabolic regulation

Publisher Summary In recent years, there has been a reawakening of interest in the physiology and biochemistry of the cell wall storage carbohydrates of seeds This chapter outlines the structures and occurrence of cell wall storage carbohydrates to give an account of current research on their metabolism and to explore their overall biological significance in the seeds which contain them Seeds are generally treated with alkali to extract polysaccharides of the “hemicellulose” type or with water to extract “gum” polysaccharides Consequently, the molecules with which this article is concerned are still widely classified as seed gums and hemicelluloses The chapter indicates the principal types of carbohydrate molecules stored in the cell walls of seeds and their distribution

François Percheron

Papers

The chitin-degrading enzyme system of a Streptomyces species.

Structure de la mannane du palmier Erythea edulis