Characterisaton of human plasma thiol proteinase inhibitors.
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.
Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, India.
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R
Das Gupta
P K
PK
Ghosh
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B
Bano
D001586:Benzoylarginine Nitroanilide / Q000378:metabolism; D001665:Binding Sites / Q000187:drug effects; D015853:Cysteine Proteinase Inhibitors / Q000097:blood / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D010206:Papain / Q000037:antagonists & inhibitors / Q000378:metabolism; D013050:Spectrometry, Fluorescence
D015853:Cysteine Proteinase Inhibitors; D001586:Benzoylarginine Nitroanilide; D010206:Papain