Substrate inhibition of cruzipain is not affected by the C-terminal domain

Endogenous and recombinant cruzipain, the major cysteine proteinase from the protozoan parasite Trypanosoma cruzi, exhibit differences in the protein and circular dichroism spectra probably attributed to the absence of the C-terminal domain in the recombinant enzyme. Substrate hydrolysis of both molecules at 25 degrees C and neutral pH obeyed Michaelis-Menten kinetics whereas significant substrate inhibition was observed above neutral pH. The results suggest that substrate inhibition of cruzipain is pH-dependent, and that the C-terminal domain does not play an essential role in this process.