Non-pancreatic hydrolysis of N-benzoyl-l-tyrosyl-p-aminobenzoic acid (PABA-peptide) in the human small intestine.

1. Hydrolysis of N-benzoyl-L-tyrosyl-p-aminobenzoic acid (PABA-peptide) has been measured in soluble and particulate fractions of human small intestinal mucosa. 2. Both soluble and particulate fractions contained enzymic activity capable of splitting the PABA-peptide. In the particulate fractions this activity increased threefold towards the distal small intestine. 3. Neither soluble nor particulate activity was inhibited by the chymotrypsin inhibitor 1-chloro-4-phenyl-3-L-toluene-p-sulphonamidobutan-2-one (TPCK). 4. Column chromatography on Sephacryl S-300 resolved a peak of PABA-peptide hydrolase activity that was clearly distinct from other known brush-border peptide hydrolases and from added chymotrypsin standard. 5. This PABA-peptide hydrolase thus represents a distinct intestinal enzyme, possibly bound to the brush-border membrane, which could account for the residual urinary PABA recovery observed in patients and animal models with exocrine pancreatic insufficiency.