Inhibition ofGlossina morsitans midgut trypsin activity byd-glucosamine

The effect of the amino sugard-glucosamine on trypsin in crude midgut homogenates ofGlossina morsitans morsitans was studied in vitro. The results showed that the midgut trypsin was specifically and competitively inhibited byd-Glucosamine. Glucose, fructose, mannose, inositol, galactose, galactosamine,N-acetyl-d-glucosamine, and methyl--d-glucosamine were ineffective as inhibitors, even at concentrations exceeding 600mm.d-glucosamine also had a similar inhibitory effect on bovine pancreatic trypsin. In both cases, the inhibition was incomplete as shown by nonlinear Dixon plots. The Michaelis and inhibition constants estimated for the midgut trypsin were 41±2 m and 68±3mm, respectively. These results suggest that the susceptibility of tsetse flies to trypanosome infection, which is associated with high midgut glucosamine levels, could be due to inhibition of trypsin or trypsin-like enzymes by this sugar.