title: Cystatin-like cysteine proteinase inhibitors from human liver.
abstract: Cysteine proteinase inhibitor (CPI) forms from human liver were purified from the tissue homogenate by alkaline denaturation of cysteine proteinases with which they are complexed, acetone fractionation, affinity chromatography on S-carboxymethyl-papain-Sepharose and chromatofocusing. The multiple forms of CPI were shown immunologically to be forms of two proteins, referred to as CPI-A (comprising the forms of relatively acidic pI) and CPI-B (comprising the more basic forms). CPI-A and CPI-B are similar in their Mr of about 12400, considerable stability to pH2, pH11 and 80 degrees C, and tight-binding inhibition of papain, several related cysteine proteinases and dipeptidyl peptidase I. Ki values were determined for papain, human cathepsins B, H and L, and dipeptidyl peptidase I. The affinity of CPI-A for cathepsin B was about 10-fold greater than that of CPI-B, whereas CBI-B showed about 100-fold stronger inhibition of dipeptidyl peptidase I. For all the cysteine proteinases the liver inhibitors were somewhat less tight binding than cystatin. The resemblance of both CPI-A and CPI-B in several respects to egg-white cystatin is discussed. CPI-A seems to correspond to the epithelial inhibitor described previously, and CPI-B to the inhibitor from other cell types [Järvinen & Rinne (1982) Biochim. Biophys. Acta 708, 210-217].
mesh_terms: D000595:Amino Acid Sequence; D002846:Chromatography, Affinity; D002851:Chromatography, High Pressure Liquid; D015853:Cysteine Proteinase Inhibitors; D006801:Humans; D005779:Immunodiffusion; D007525:Isoelectric Focusing; D007700:Kinetics; D008099:Liver / Q000032:analysis*; D011480:Protease Inhibitors / Q000302:isolation & purification; D011506:Proteins / Q000302:isolation & purification
chemical_list: D015853:Cysteine Proteinase Inhibitors; D011480:Protease Inhibitors; D011506:Proteins