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Protozoa of the family Trypanosomatidae are pathogenic agents of human and animal diseases. Fine structure, compaction pattern, and histone content of the soluble chromatin were investigated in procyclic forms of Trypanosoma cruzi (Chagas disease, S. America) and T. brucei brucei (Nagana disease, Africa) in comparison with rat liver chromatin. At low ionic strength chromatin was present as nucleosome filaments. Condensation into compact fibers (solenoid) was complete for rat chromatin at 100 mM salt concentration while chromatin of T. cruzi showed less condensation (tangle formation), and that of T.b. brucei did barely condense under identical experimental conditions. In general, the nucleosomes of trypanosomes, especially T.b. brucei, seemed to be less regularly arranged than those of the higher eukaryote. Addition of histone H1-containing fractions of rat liver chromatin increased the compaction of T. cruzi chromatin but had no influence on T.b. brucei chromatin. SDS-polyacrylamide gel electrophoresis revealed histone H1 and the 4 core histones in rat liver chromatin. Neither in T. cruzi nor T.b. brucei were proteins identical to rat histone H1 present. Differences existed also in molecular weight of core histones between rat and trypanosomes, as well as between T. cruzi and T.b. brucei. These differences might explain species-specific differences in the fine structural organization and compaction pattern of the chromatin of the rat, T. cruzi, and T.b. brucei.

The activities of trypsin, aminopeptidase, and alpha-glucosidase were studied in the whole midgut, anterior and posterior midgut, and posterior midgut lumen and epithelium of the mosquito Anopheles stephensi Liston. Trypsin activity was restricted entirely to the posterior midgut lumen. No trypsin activity was found before the blood meal, but activity increased continuously up to 30 h after feeding, and subsequently returned to baseline levels by 60 h. Aminopeptidase was active in anterior and posterior midgut regions before and after feeding. In whole midguts, activity rose from a baseline of approximately 3 enzyme units (EU) per midgut to a maximum of 12 EU at 30 h after the blood meal, subsequently falling to baseline levels by 60 h. A similar cycle of activity was observed in the posterior midgut and posterior midgut lumen, whereas aminopeptidase in the posterior midgut epithelium decreased in activity during digestion. Aminopeptidase in the anterior midgut was maintained at a constant low level, showing no significant variation with time after feeding. alpha-glucosidase was active in anterior and posterior midguts before and at all times after feeding. In whole midgut homogenates, alpha-glucosidase activity increased slowly up to 18 h after the blood meal, then rose rapidly to a maximum at 30 h after the blood meal, whereas the subsequent decline in activity was less predictable. All posterior midgut activity was restricted to the posterior midgut lumen. Depending upon the time after feeding, greater than 25% of the total midgut activity of alpha-glucosidase was located in the anterior midgut. The enzyme distributions are consistent with described structural models for digestion in mosquitoes. After blood meal ingestion, proteases are active only in the posterior midgut. Trypsin is the major primary hydrolytic protease and is secreted into the posterior midgut lumen without activation in the posterior midgut epithelium. Aminopeptidase activity is also luminal in the posterior midgut, but cellular aminopeptidases are required for peptide processing in both anterior and posterior midguts. alpha-glucosidase activity is elevated in the posterior midgut after feeding in response to the blood meal, whereas activity in the anterior midgut is consistent with a nectar-processing role for this midgut region.

The presence and distribution of binding sites for eight different lectins, Con A, DBA, HPL, LFA, RCA I, SBA, UEA I, and WGA, were compared in the midguts of Plasmodium gallinaceum-infected Aedes aegypti and Plasmodium berghei-infected Anopheles stephensi. Lectins with high specificity for N-acetyl-D-glucosamine (GlcNAc) exhibited high binding preference for the peritrophic membrane and microvillar glycocalyx of Ae. aegypti; the same structures were preferentially labeled by N-Acetyl-D-galactosamine (GalNAc)-specific lectins in An. stephensi. No differences could be observed in the lectin-binding patterns of the intercellular spaces or cellular organelles and structures. The Plasmodium ookinete surface did not react with any of the lectins tested. It appears that sugars are involved in vector recognition by the parasite and that the peritrophic membrane and/or glycocalyx may be crucial structures for the penetration of the gut epithelium by the ookinete.