(2006). The midgut of P. nigrispinus, like other Heteroptera Pentatomorpha (see for example D. peruvianus, Silva et al., 1995), is divided into three major chambers, from which the first (AM, anterior midgut) and the last (PM, posterior midgut) are dilated and the middle chamber (MM, middle midgut) is cylindrical ( Fig. 1B). Salivary and midgut luminal contents are mildly acidic. The mean selleckchem and standard errors of pH values (n = 10) are 6.0 ± 0.1 in salivary gland and 5.6 ± 0.1 in AM, 5.7 ± 0.1 in MM, and 5.8 ± 0.1 in PM. The fine structure of P. nigrispinus

midgut cells do not differ much from other Heteroptera Pentatomomorpha, like D. peruvianus ( Silva et al., 1995) and Brontocoris tabidus (Heteroptera: Pentatomidae) ( Guedes et al., 2007 and Fialho

et al., 2009). Hence, only the apical features that are interesting in the context of this work will be described. The apex of midgut cells display microvilli that are ensheathed with glove-like finger membranes, the perimicrovillar membranes (Fig. 2A and B). What are remarkable are the muscles fibers visible in the midgut lumen (Fig. 2C and D). These ingested muscles fibers are discernible only in the anterior and middle midgut, suggesting that they are digested as the food moves toward the hindgut. Activities measured in extracts of midguts and salivary glands are described in table 1. The substrate Suc-AAPF-MCA was not hydrolyzed by homogenates of salivary glands and midguts, thus ruling out the occurrence of chymotrypsin as a digestive enzyme. Z-FR-MCA (like benzoyl-Arg-p-nitroanilide, BApNA) may be hydrolyzed by both cathepsin L-like enzymes, which are cysteine proteinases, and trypsin, which is a serine proteinase. They may be GSK126 in vivo distinguished, however, by their pH optima and their response in the presence of sulfhydryl reagents (usually Cys) and E-64 (Terra and Ferreira, 1994). By these criteria, the major proteinase in both salivary glands and midgut is cathepsin L, although a small amount of trypsin activity is present in salivary glands. These conclusions are based in the following

observations: (1) assays with Z-FR-MCA at pH 6.0 in the presence of Amino acid Cys were strongly inhibited by E-64 (100 ± 10% in midguts and 92 ± 7% in salivary glands), revealing the presence of a cathepsin L activity; (2) assays with Z-FR-MCA at pH 7.5 with salivary gland homogenates were inhibited by only 31 ± 8% in the presence of E-64, indicating the occurrence of a trypsin activity. No activity was found at those conditions in midgut samples, discounting the presence of significant trypsin activity in midguts. Activity on Z-RR-MCA is only 2% of the activity determined with Z-FR-MCA, confirming that the enzyme is really a cathepsin L, discounting the possibility of being a cathepsin B (also a cysteine proteinase), which would be more activity on Z-RR-MCA (Barrett et al., 2004). Enzyme activities determined with native collagen (thus presenting a triple helix) correspond to the metalloproteinase collagenase.