Proteolytic enzymes and blood digestion in the mosquito,Culex nigripalpus

The synthesis of proteolytic enzymes in the fat body and midgut of female Culex nigripalpus was followed. The effects of brain factor(s) and RNA levels in the fat body were correlated with the synthesis of proteolytic enzymes. Trypsinlike activity in the midgut of C. nigripalpus accounted for 80% of total proteolytic activity, whereas chymotrypsinlike activity accounted for 5–7% of total proteolytic activity. Synthesis of porteases in the midgut and fat body reached a peak at 35 h and 22 h after the blood meal, respectively. In the fat body, proteolytic enzyme activity fell to a low level 30 h after the blood meal, but activity in the midgut reached a low level 58 h after the blood meal. The presence of low protease activity in the fat body at the time of peak vitellogenin synthesis indicated that processing of vitellogenin was not done in this tissue. Fat bodies incubated in vitro in the presence of ¹⁴C]valine synthesized a ¹⁴C]labeled trypsinlike molecule identified as such with antitrypsin antibodies and specific substrate p-toluene-sulphonyl-L-arginine methylester (TAME) and on disc gel electrophoresis in the presence of dodecyl sulfate. The sizes of the proteins found inside and outside the peritrophic membrane were determined by gel-chromatography and disc gel electrophoresis in the presence of dodecyl sulfate. The molecular weight (± SEM) of the largest polypeptide that migrated through the peritrophic membrane into the ectoperitrophic space was found to be 23,000 ± 2,000 daltons. Based on these results, a model is proposed to account for blood digestion in the mosquito midgut, along with the role of the peritrophic membrane.