Characterisaton of human plasma thiol proteinase inhibitors.
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1998-12-21
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Earlier, we had reported purification of three thiol proteinase inhibitors (TPI-1 of 70 kDa, TPI-3 of 195 kDa and TPI-4 of 497 kDa) from human plasma. In the present study we report that TPI-1 binds to papain in the stoichiometry ratio (E/I) of 1:1 while TPI-3 and TPI-4 bind in the ratio of 1.5:1 and 3.2:1 respectively. The K(m) for papain with BAPNA as substrate and Kcat/K(m) values for TPI-1, TPI-3 and TPI-4 were 2.7 x 10(-6) M, 0.84 nM/sec; 3.2 x 10(-6) M, 0.75 nM/sec; and 3.6 x 10(-6) M, 0.72 nM/sec respectively. The Ki values were found to be 1.48 nM for TPI-1, 0.133 nM for TPI-3 and 0.117 nM for TPI-4. The UV absorption and fluorescence emission spectra study suggest involvement of aromatic residues in the binding process. This study suggests that TPI-4 is the most potent inhibitor of thiol proteinases.
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Das Gupta R, Ghosh PK, Bano B. Characterisaton of human plasma thiol proteinase inhibitors. Indian Journal of Biochemistry & Biophysics. 1998 Dec; 35(6): 377-81