title: Three forms of thiol proteinase inhibitor from rat liver formed depending on the oxidation-reduction state of a sulfhydryl group.
abstract: Three forms of a thiol proteinase inhibitor were isolated from rat liver cytosol. The monomeric inhibitor (pI 5.2) (TPI-1) formed a complex with cathepsin H even in the absence of reducing agents. The inhibitor with pI 5.0 (TPI-2) was inactive in the absence of reducing agents but was converted to an active inhibitor on addition of reducing agents such as dithiothreitol, GSH, cysteine, or 2-mercaptoethanol. The dimeric inhibitor (TPI-D) with an intermolecular disulfide bridge was also inactive and was converted to the active monomeric inhibitor on addition of dithiothreitol. TPI-2 is most likely a mixed disulfide with glutathione. One (Cys-3) of two cysteine residues exposed on the surface of the molecule of TPI-2 is involved in the formation of a mixed disulfide, and the other cysteine residue (Cys-64) is buried in the molecule. The activity of rat liver thiol proteinase inhibitor may possibly be regulated by formation of a protein mixed disulfide or by reduction of the mixed disulfide.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D056655:Cathepsin H; D002403:Cathepsins / Q000378:metabolism; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D003545:Cysteine / Q000032:analysis; D003546:Cysteine Endopeptidases; D005978:Glutathione / Q000032:analysis; D007527:Isoenzymes / Q000032:analysis; D008099:Liver / Q000737:chemistry*; D008297:Male; D008970:Molecular Weight; D010084:Oxidation-Reduction; D011480:Protease Inhibitors / Q000032:analysis*; D011487:Protein Conformation; D051381:Rats; D011919:Rats, Inbred Strains; D013438:Sulfhydryl Compounds / Q000032:analysis*
chemical_list: D000596:Amino Acids; D007527:Isoenzymes; D011480:Protease Inhibitors; D013438:Sulfhydryl Compounds; D002403:Cathepsins; D003546:Cysteine Endopeptidases; D056655:Cathepsin H; C534128:Ctsh protein, rat; D005978:Glutathione; D003545:Cysteine