Partial purification and properties of urinary thiol proteinase inhibitors

The urinary thiol proteinase inhibitors u-TPI1 and u-TPI2 were partially purified from human urine by gel filtration on Sephadex G-50 and Sephadex G-100 columns, and affinity chromatography on a trypsin.chymotrypsin-Chromagel A-2 column. They showed similar inhibition spectra to that of plasma inhibitors, inhibiting ficin strongly and papain moderately, but not inhibiting trypsin and chymotrypsin. The molecular weights of u-TPI1 and u-TPI2 were determined to be 76,000 and 22,500 by gel filtration on Sephadex G-150 and G-75, respectively, and their isoelectric points were found to be 4.6 and 4.8 by isoelectrofocusing. u-TPI1 and u-TPI2 were labile at acidic pH, but stable at neutral and alkaline pH. Both inhibitors were relatively thermostable, showing no decrease in activity on heating up to 50 degrees C for 1 h. The antibody against plasma thiol proteinase inhibitor alpha1-TPI suppressed the activities of the urinary inhibitors significantly, and on double immunodiffusion formed clear precipitin lines with both u-TPI1 and u-TPI2. On immunoelectrophoresis u-TPI1 migrated in the alpha 2-region and u-TPI2 in the beta 1-region. It is concluded from these data that the urinary thiol proteinase inhibitors are degradation products of the plasma inhibitors.