Human Urinary Proteinase Inhibitor: Inhibitory Properties and Interaction with Bovine Trypsin

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Abstract
The major urinary trypsin inhibitor (UTI) was found to inhibit bovine chymotrypsin and human leukocyte elastase strongly, cathepsin G weakly. No inhibition of porcine pancreatic elastase was observed. The stoichiometry of the inhibition of bovine trypsin by UTI was determined spectrophotometrically to be 1:2 (I/E molar ratio). After incubation of UTI with this enzyme in various molar ratios, 2 complexes (C1 and C2) could be visualized in alkaline polyacrylamide gel electrophoresis. C1 was isolated by affinity chromatography on Con-A Sepharose. In dodecyl sulfate polyacrylamide gel electrophoresis, C1 was dissociated to give an inhibitory band with the same electrophoretic mobility as native UTI. C2 released an active inhibitory fragment with MW near 20,000. A time-course study demonstrated that a molar ratio I/E of 1.5:1, the C2 complex appears after 2 h of incubation.