Figure 2

Active-site titration of digestive peptidases in the Ixodes ricinus gut tissue extracts during feeding on the host. The groups of 15-20 females were forcibly removed and collected from four guinea pigs at the indicated feeding time points. The guts from individual ticks were subsequently dissected and the gut tissue extracts were prepared from the pool of longitudinally cut midgut halves. The absolute molarities of the individual peptidases in gut homogenates were determined by stoichiometric titration with the appropriate active-site inhibitors (Table 1). Bars represent the average value from a triplicate measurement. Standard deviations were ≤10% of the average value and are not shown. The molarity of cathepsin L (IrCL) was not determined because an appropriate inhibitor was lacking. For details, see Material and Methods section.