Purification and physicochemical studies of human plasma thiol proteinase inhibitors

The physicochemical properties of thiol proteinase inhibitors (TPI) isolated from outdated human blood have been studied. A simple technique which includes ammonium sulphate precipitation, Sephadex G-200 gel filtration and ion-exchange chromatography led to the isolation of 4 isolates namely TPI-1, TPI-2, TPI-3 and TPI-4 having molecular mass of 70, 155, 195 and 497 kDa respectively. The latter two forms are the new isolates unreported previously. They exhibit similar pH stability, inhibition spectra with papain, cathepsin B and trypsin, antigenic properties and glycoprotein nature. The TPI-4, however, was found to be most heat stable showing no decrease in inhibitory activity when heated upto 70 degrees C for 30 min. Our work suggests that TPI-3 and TPI-4 are the oligomers of TPI-1.