African animal trypanosomosis (nagana) is caused by tsetse-transmitted protozoan parasites. Their cysteine proteases are potential chemotherapeutic and diagnostic targets. The N-glycosylated catalytic domain of Trypanosoma vivax cathepsin L-like cysteine protease, rTviCATLcat, was recombinantly expressed and purified from culture supernatants while native TviCATL was purified from T. vivax Y486 parasite lysates. Typical of Clan CA, family C1 proteases, TviCATL activity is sensitive to E-64 and cystatin and substrate specificity is defined by the S2 pocket. Leucine was preferred in P2 and basic and non-bulky, hydrophobic residues accepted in P1 and P3 respectively. Reversible aldehyde inhibitors, antipain, chymostatin and leupeptin, with Arg in P1 and irreversible peptidyl chloromethylketone inhibitors with hydrophobic residues in P2 inhibited TviCATL activity. TviCATL digested host proteins: bovine haemoglobin, serum albumin, fibrinogen and denatured collagen (gelatine) over a wide pH range, including neutral to slightly acidic pH. The recombinant catalytic domain of TviCATL showed promise as a diagnostic target for detecting T. vivax infection in cattle in an indirect antibody detection ELISA.Read less <