We have previously described a bloodmeal-induced molecule (lectin-trypsin complex) from the midgut of the tsetse fly, Glossina longipennis, with both lectin and trypsin activities (Osir et al., 1995). In this paper, we report on the isolation of a similar molecule from the midguts of Glossina fuscipes fnscipes and provide direct evidence for its involvement in the development of African trypanosomes. The molecule (native Mr ∼65,700) has two non-covalently linked subunits, Mr ∼28,800 and Mr ∼35,700. The native molecule was found to be capable of inducing differentiation of bloodstream-form trypanosomes into procyclic (midgut forms) in vitro. In the assays, specific antibodies against procyclin were used to monitor the transformation of the bloodstream-form trypanosomes into procyclic forms. This induction was specifically inhibited by D-glucosamine. Cis-aconitate was also capable of inducing the transformation process with the same efficiency as that of the lectin-trypsin complex. While increasing the concentrations of the lectin-trypsin complex (≥100 μg protein/ml) in the incubation assays resulted into higher transformation rates, it also led to high parasite mortality. These results provide evidence for the involvement of the midgut lectin-trypsin complex in the differentiation of bloodstream-form trypanosomes within tsetse midgut.

—Midgut trypsin and lectin levels were determined in three tsetse species, namely Glossina morsitans morsitans, G. longipennis and G. fuscipes fuscipes. In addition, the abilities of midgut homogenates prepared from these flies to transform bloodstream-form Trypanosoma brucei brucei and T. congolense were compared in vitro. In all the species examined, trypsin levels did not differ significantly up to 24 h post-bloodmeal. There were similar rates of transformation of the bloodstream-form trypanosomes into procyclic (midgut) forms in vivo, so that all species had similar levels of infection in the midgut. However, trypsin levels continued to increase beyond 24 h, reaching a peak between 48 and 72 h. The peak was lowest in G. m. morsitans. The midgut homogenates in this species also had the lowest levels of lectin. The species had the highest levels of mature T. congolense and T. brucei infections. We propose that the lower levels of peak midgut tryspin and lectin in G. m. morsitans is important in the establishment of trypanosome infections in this species of tsetse.

Activity of digestive enzymes (trypsin, chymotrypsin and amylase) was studied in relation with food in Penaeus vannamei larvae first stages. Microparticles containing casein involved the decrease of soluble protein content and enzyme activities. Specific trypsin activity but not chymotrypsin was correlated (p < 1%) to casein level between 10 and 60% in microparticles. Cellulose fibres in food seemed to have little effect on digestive enzymes. Starch, between 1 and 20% in microparticles, had no influence on specific amylase activity. The effect of different feeding conditions were also tested on growth. No clear relationship between growth and enzyme is established since only trypsin is concerned in the case of a casein dose effect in the food. The protein source (casein, gelatin, squid meal or fish protein soluble concentrate) as well as the carbohydrate quality (soluble starch, standard corn starch, amylopectin corn starch or pregelatinized corn starch) were tested. Squid meal stimulated significantly chymotrypsinactivity (p < 2%) while trypsin activity decreased with fish protein soluble concentrate p < 5%). Source of carbohydrate seemed very important, amylase activity increased significantly ( p < 2%) with corn starch. These adaptations are not correlated to growth performances since squid meal or fish protein soluble concentrate improved larval development until zoe 3 substage. These results suggest a specific induction of digestive enzymes to the food quality in larvae independent of growth performances.