A trypsin inhibitor was identified in extracts of adult Trichuris suis and
culture fluids from 24-h in vitro cultivation of adult parasites. The inhib
itor was isolated by acid precipitation, affinity chromatography (trypsin-a
garose), and reverse phase HPLC as a single polypeptide with a molecular we
ight estimated at 6.6 kDa by laser desorption mass spectrometry. The purifi
ed inhibitor associated strongly with trypsin (equilibrium dissociation inh
ibitory constant (K-i) of 3.07 nM) and chymotrypsin (K-i = 24.5 nM) and was
termed TsTCI. Elastase, thrombin, and factor Xa were not inhibited. The cD
NA-derived amino acid sequence of the mature TsTCI consisted of 61 residues
including 8 cysteine residues with a molecular mass of 6.687 kDa. The N-te
rminal region of TsTCI (46 residues) showed limited homology (36%) to a pro
tease inhibitor from the hemolymph of the honeybee Apis mellifera, which is
considered to be a member of the Ascaris inhibitor family. However, TsTCI
did not display sequence homology with other members of this family or the
distinctive cysteine residue pattern which distinguishes this family. Howev
er, similarity of a region of TsTCI (11 residues) with the reactive site re
gions of inhibitors from the nematodes Ascaris suum, Anisakis simplex, and
Ancylostoma caninum was apparent.