No abstract

Bostrichiformia is the less known major series of Coleoptera regarding digestive physiology. The midgut of Dermestes maculatus has a cylindrical ventriculus with anterior caeca. There is no cell differentiation along the ventriculus, except for the predominance of cells undergoing apocrine secretion in the anterior region. Apocrine secretion affects a larger extension and a greater number of cells in caeca than in ventriculus. Ventricular cells putatively secrete digestive enzymes, whereas caecal cells are supposed to secrete peritrophic gel (PG) glycoproteins. Feeding larvae with dyes showed that caeca are water-absorbing, whereas the posterior ventriculus is water-secreting. Midgut dissection revealed a PG and a peritrophic membrane (PM) covering the contents in anterior and posterior ventriculus, respectively. This was confirmed by in situ chitin detection with FITC-WGA conjugates. Ion-exchange chromatography of midgut homogenates, associated with enzymatic assays with natural and synthetic substrates and specific inhibitors, showed that trypsin and chymotrypsin are the major proteinases, cysteine proteinase is absent, and aspartic proteinase probably is negligible. Amylase and trypsin occur in contents and decrease along the ventriculus; the contrary is true for cell-membrane-bound aminopeptidase. Maltase is cell-membrane-bound and predominates in anterior and middle midgut. Digestive enzyme activities in hindgut are negligible. This, together with dye data, indicates that enzymes are recovered from inside PM by a posterior-anterior flux of fluid outside PM before being excreted. The combined results suggest that protein digestion starts in anterior midgut and ends in the surface of posterior midgut cells. All glycogen digestion takes place in anterior midgut.

Sugarcane is an important crop that has recently become subject to attacks from the weevil Sphenophorus levis, which is not efficiently controlled with chemical insecticides. This demands the development of new control devices for which digestive physiology data are needed. In the present study, ion-exchange chromatography of S. levis whole midgut homogenates, together with enzyme assays with natural and synthetic substrates and specific inhibitors, demonstrated that a cysteine proteinase is a major proteinase, trypsin is a minor one and chymotrypsin is probably negligible. Amylase, maltase and the cysteine proteinase occur in the gut contents and decrease throughout the midgut; trypsin is constant in the entire midgut, whereas a membrane-bound aminopeptidase predominates in the posterior midgut. The cysteine proteinase was purified to homogeneity through ion-exchange chromatography. The purified enzyme had a mass of 37 kDa and was able to hydrolyze Z-Phe-Arg-MCA and Z-Leu-Arg-MCA with k(cat)/K(m) values of 20.0±1.1 μM(-1)s(-1) and 30.0±0.5 μM(-1)s(-1), respectively, but not Z-Arg-Arg-MCA. The combined results suggest that protein digestion starts in the anterior midgut under the action of a cathepsin L-like proteinase and ends on the surface of posterior midgut cells. All starch digestion takes place in anterior midgut. These data will be instrumental to developing S. levis-resistant sugarcane.

Neotropical Entomology 35(2): 215-222 (2006) Bases Biológicas, Nutricionais e Histoquímicas para o Aprimoramento de Dieta Artificial para Bracon hebetor Say (Hymenoptera: Braconidade) PALAVRAS-CHAVE: Controle biológico, ácido graxo, idiobionte, exigência nutricional, proteínaABSTRACT -The biology of Bracon hebetor Say (Hymenoptera: Braconidae) reared on fifth instars of Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae) (natural diet) and in vitro (artificial diet) was evaluated. Data on the number of instars, development time and food intake were collected, and histochemical tests were conducted to detect proteins and lipids in the parasitoid's digestive tract. The data disclosed differences that can help to improve artificial rearing of B. hebetor. B. hebetor had three instars in both diets, but the developmental time on the artificial diets was prolonged due to the increase in larval and pupal development times. Larvae grew faster on the natural host and required a lower food intake (2.7 μl) as compared to that required by the larvae feeding on the artificial diet (3.8 μl). Analysis of diet protein content and host hemolymph and the observations on the parasitoid larvae gut content indicated altogether the artificial diets requires the addition of others sources of proteins and lipids to improve the overall nutrition quality of the in vitro rearing system for this ectoparasitoid.

Chlorate reductase has been purified from the chlorate-metabolizing bacterium Ideonella dechloratans. The enzyme is a trimeric aPy complex with an apparent Mr of 160 000. The a, p, and y subunits are 94 kDa, 35,5 kDa and 27 kDa, respectively, in size. The presence of a molybdenum cofactor was demonstrated by fluorimetric analysis of the oxidized form A of molybdopterin.The enzyme contained 1,3 mol molybdopterin / mol enzyme. Pyridine hemochrome spectra revealed the presence of 0,6 mol cytochrome b/ mol enzyme. The enzyme also reduced bromate, iodate, nitrate and selenate. The rates of reduction (relative to that of chlorate) were 107%, 21%, 16% and 7%, respectively. The similarity of the enzyme to GR-1 chlorate reductase, chlorate reductase C, selenate reductase, nitrate reductases and TMAO/DMSO reductases is discussed.