Publisher Summary The aim of this chapter is to review the recent and spectacular progress in the study of insect digestive biochemistry. It tries to establish uniform parameters for studying insect digestive enzymes, providing an overview of the biochemistry of insect digestion, and discusses factors affecting digestive enzymes in vivo . It reviews digestive enzymes and microvillar proteins, with the emphasis on molecular aspects. Further it describes the details of the digestive biochemical process alongside insect evolution and discusses data on digestive enzyme secretion mechanisms. Digestion is the process by which food molecules are broken down into smaller molecules that are absorbed by cells in the gut tissue. This process is controlled by digestive enzymes and is dependent on their localization in the insect gut. Enzyme kinetic parameters are meaningless unless assays are performed in conditions in which enzymes are stable. If researchers adopt uniform parameters and methods, comparisons among similar and different insect species will be more meaningful.

Biochemistry and Molecular Biology of Digestion

4.5 – Biochemistry of Digestion

http://directory.umm.ac.id/Data%20Elmu/jurnal/I/Insect%20Biochemistry%20and%20Molecular%20Biology/Vol30.Issue12.Dec2000/916.pdf

Purification and properties of a β-glycosidase purified from midgut cells of Spodoptera frugiperda (Lepidoptera) larvae

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1002/2211-5463.12097

Effect of Tris, MOPS, and phosphate buffers on the hydrolysis of polyethylene terephthalate films by polyester hydrolases

Digestive proteinases and carbohydrases of Ectomyelois ceratoniae (Zeller) larvae were investigated using appropriate substrates and inhibitors. Midgut pH in larvae was determined to be slightly alkaline. Midgut extracts showed optimum activity for proteolysis of hemoglobin at pH 9?12. Midgut proteinases also hydrolyzed the synthetic substrates of trypsin, chymotrypsin, and elastase at pH 8?11. Maximum digestive α-amylase activity was also observed at pH 8?11. However, optimum activity for α- and β-glucosidase occurred at pH 5?8. Alpha- and β-galactosidases optimum activities occurred at pH 5 and pH 6, respectively. Inhibitors of serine proteases were effective on midgut serine proteases (trypsin and chymotrypsin proteases). Zymogram analyses revealed at least five bands of total proteolytic activity in the larval midgut. Proteasespecific zymogram analyses revealed at least four, two, and one isozymes for trypsin-, chymotrypsin-, and elastase-like activities respectively. Two α-amylase isozymes were found in the midgut of fifth instar larvae and in the whole bodies of 1st through 5th instar larvae. Zymogram studies also revealed the presence of one and two bands of activity for β- and α-glucosidase, respectively. Recycling of α-amylase and proteases in the larval midgut was not complete. At least one isozyme of trypsin, chymotrypsin, elastase, and α-amylase were not recycled and were observed in the larval hindgut.

Biochemical characterization of digestive proteases and carbohydrases of the carob moth, Ectomyelois ceratoniae (Zeller) (Lepidoptera: Pyralidae)

There are three midgut α-galactosidases (TG1, TG2, TG3) from Tenebrio molitor larvae that are partially resolved by ion-exchange chromatography. The enzymes have approximately the same pH optimum (5.0), pl value (4.6) and Mr value (46 000–49 000) as determined by gel filtration or native electrophoresis run in polyacrylamide gels with different concentrations. Substrate specificities and functions were proposed for the major T. molitor midgut α-galactosidases (TG2 and TG3) based on chromatographic, carbodiimide inactivation, Tris inhibition, and on substrate competition data. Thus, TG2 would hydrolyse α-1,6-galactosaccharides, exemplified by raffinose, whereas TG3 would act on melibiose and apparently also on digalactosyldiglyceride, the most important compound in the thylacoid membranes of chloroplasts. Most galactoside digestion should occur in the lumen of the first two thirds of T. molitor larval midguts, since α-galactosidase activity predominates there. Spodoptera frugiperda larvae have three midgut α-galactosidases (SG1, SG2, SG3) partially resolved by ion-exchange chromatography. The enzymes have similar pH optimum (5.8), pl value (7.2) and Mr value (46 000–52 000), and at least the major α-galactosidase must have an active carboxyl group in the active site. Based on data similar to those described for T. molitor, SG1 and SG3 should hydrolyse melibiose and SG3 should digest raffinose and, perhaps, also digalactosyldiglyceride. The midgut distribution of α-galactosidase activity supports the proposal that α-galactosidase digestion occurs at the surface of anterior midgut cells in Spodoptera frugiperda larvae.

Gisele A. Grossmann

Papers

α-Galactosidases from the larval midgut of Tenebrio molitor (Coleoptera) and Spodoptera frugiperda (Lepidoptera)