The protozoan Trypanosoma cruzi that causes South American trypanosomiasis expresses peptidases during its entire parasitic life cycle. Understanding better the function and specificity of the peptidases may lead to new inhibitors and potential therapies. It has been shown this alkaline peptidase has a preference for basic amino acids at position one and position two of the substrate. The sequence Leu-Gly-Arg was shown to have a high Km and high Vmax compared to other peptides tested.

Provided here is a fluorogenic peptide substrate for Trypanosoma cruzi alkaline peptidase. In its entire state, this peptide is not fluorescent. However, this peptide is cleaved by T. cruzi alkaline peptidase. Upon rhodamine 110 fluorophore release, fluorescence can then be detected. This peptide, therefore, allows for the quantification of T. cruzi alkaline peptidase activity. Rhodamine 110 is a widely used red fluorescent probe.