Anterior midgut proteinase inhibitor from Glossina morsitans morsitans Westwood (Diptera: Glossinidae) and its effects upon tsetse digestive enzymes

Abstract

The anterior midgut of Glossina morsitans morsitans Westwood contains a proteinase inhibitor, molecular weight 5000 ± 2000daltons, stable to 1 M HCl, heat, and dialysis, but unstable to 1% trichloroacetic acid. Inhibitor activity is not associated with anticoagulant in the anterior midgut. The specific activity of the proteinase inhibitor is similar in mated and unmated females and greater than in male tsetse flies. Proteinase inhibitor inhibits proteinase VI and trypsin hydrolysis of N-benzoyl-L-arginine ethyl ester (BAEE) and benzoyl-DL-arginine-p-nitroanilide (BAPNA) but has no effect on proteinase VI hydrolysis of haemoglobin. Inhibition of trypsin hydrolysis of haemoglobin is noncompetitive. Proteinase inhibitor levels in the anterior midgut decreased immediately after feeding and then increased, reaching a maximum 60–100 h after ingestion of the bloodmeal. Postteneral flies contained higher levels of proteinase inhibitor than teneral individuals. Trypsin activity in gut homogenates of Phormia regina and Aedes aegypti was inhibited by the tsetse inhibitor. There was no detectable inhibition of bovine or Pterostichus adstrictus trypsin activity. Inhibition of Periplaneta americana trypsin occurred but was less than fly trypsin inhibition. The possible role of the inhibitor in terminating proteinase production is discussed.