Activity profiling of I. ricinus gut peptidases. Peptidolytic activities in the gut tissue extract of partially engorged tick females (the 5-th day of feeding) were demonstrated in vitro with selective peptide substrates (structure of the fluorogenic substrates is indicated). The activity for individual substrates was suppressed in the presence of selective peptidase inhibitors to obtain diagnostic responses indicative of a protease type. Values are expressed as percent inhibition of the control activities. The identified major activities (Target) correspond to papain-type peptidases cathepsin B, L and C (CathB, CathL and CathC, respectively), cathepsin D-like aspartic peptidase (CathD) and asparaginyl endopeptidase (AE). The assay was performed at pH 4.0, an optimum pH for hemoglobin degradation by the gut extract. The activity of AE and CathL was measured in the presence of CA-074 inhibitor to prevent an interference with the activity of CathB. The error bars indicate standard deviations of the mean of triplicates.