About this Research Topic
Insects obtain their nutritional requirements by utilizing food from environment and proper digestion of ingested food. Digestion following ingestion of food from various origins is a process by which food molecules (macromolecules such as carbohydrates, lipids and proteins) are broken down into smaller molecules to be absorbed by cells in the gut tissue. The ingested foods by insects are polymers such as starch, proteins and lipids that are digested in three phases. Primary digestion is the dispersion and reduction in molecular size of the polymers leading to oligomers. During intermediate digestion, a further reduction is made, producing smaller molecules (dimers), and then dimers become monomers as the final step. This process is perfectly controlled by digestive enzymes that depend on their site of activity in the insect gut. The major digestive enzymes in the midgut of insects consist of amylases, glycosidases, lipases and proteases that are similar in their hydrolytic nature. α-Amylases (α-1,4-glucan-4-glucanohydrolases; EC 22.214.171.124) are the hydrolytic enzymes that catalyze the hydrolysis of α-D-(1,4)-glucan linkages in glycogen and other related carbohydrates. Glycosidases (EC 3.2) catalyze cleavage of internal bonds in polysaccharides and hydrolyze oligosaccharides as well as disaccharides. Lipases (triacylglycerol-acyl-hydrolase EC 126.96.36.199), which catalyse the hydrolysis of fatty acid ester bonds, are widely distributed among animals, plants and microorganisms. The most characteristic property of lipases is their activity on substrates at the interface between the aqueous and the lipid phase. Peptidases (peptide hydrolases, EC 3.4) act on peptide bonds and include proteinases (endopeptidases, EC 3.4.21–24) and exopeptidases (EC 188.8.131.52–19).
Since synthetic insecticide lead to various problem in ecosystem and agricultural production, researches trends on digestive physiology of insects. There are numerous studies showing effect of specific inhibitors, especially amylases and proteases, on digestive enzymes lead to suppress their activity and overall disruption of digestive process. Many of these inhibitors is now used in resistance or transgenic plants. In fact, creating resistant varieties using a biotechnological approach has led to the development of insect-resistant transgenic plants through the transfer of several insect resistance genes to suppress insect growth. It is mandatory to study insect pests’ digestive enzymes in order to develop biotechnological processes to provide resistant host plants. The digestive enzymes of insects could be a target to overcome their feeding ability so their developmental secretion and site of activity in the insect gut needs specific attention. The last similar review comes back to 2005 by Terra and Ferriera “Terra WR, Ferreira C. 2005. Biochemistry of digestion. In: Gilbert LI, Iatrou K, Gill SS, editors. Comprehensive molecular insect science, vol. 3. San Diego, California, USA: Elsevier. pp. 171–224.” So a new research gate in case seems to be necessary.
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