Porcine intestinal peptidase

Inpro 90 WPI was purchased from Vitalus (Abbotsford, BC), with the following composition: protein (dry basis) ≥92%; β-lactoglobulin (β-LG) 43%–48%; GMP 24%–28%; α-lactalbumin 14%–18%; bovine serum albumin (BSA) 1%–2%; immunoglobulins 1%−3%; lactoferrin <1%. Pepsin from porcine stomach mucosa, porcine pancreatic trypsin, bovine pancreatic chymotrypsin, porcine intestinal peptidase, pancreatin from porcine pancreas, and O-phthalaldehyde (OPA), were purchased from Sigma-Aldrich. Amicon regenerated cellulose ultrafiltration membranes of Molecular Weight Cut-Off (MWCO) 1 and 10 kDalton (kDa) and ultrafiltration stirred units were purchased from Millipore. Bradford reagent was purchased from BD Biosciences. Ferric chloride was purchased from ACP Chemicals Inc., l-ascorbic acid was bought from Fisher Scientific. Sodium acetate trihydrate, glacial acetic acid and 2,4,6-tri(2-pyridyl)-s-triazine (TPTZ) were purchased from Sigma-Aldrich. All other chemicals were purchased from Sigma-Aldrich and were of highest analytical grade.

Standard multi-ionic solution for plasma spectrometry is from Perkin-Elmer, Waltham, MA, USA. N-benzoyl-DL-arginine, +catechin, p-nitroanilide, β-glucosidase, bacterial protease, porcine pancreatic trypsin, bovine pancreatic α-chymotrypsin, porcine intestinal peptidase, trypsin, boron trifluoride, and vainillin were from Sigma (Sigma Chemical Co., St Louis, MO, USA). All the other chemicals were of analytical grade.