title: A catalytically active high-Mr form of human cathepsin B from sputum.
abstract: A cysteine proteinase from purulent sputum was partially purified by a method involving affinity chromatography on Sepharose-aminohexanoylphenylalanylglycinaldehyde semicarbazone. It was immunologically related to lysosomal cathepsin B from human liver and was similar in many, but not all, other aspects. It was catalytically active, as demonstrated by active-site-directed radioiodination, and hydrolysed three cathepsin B substrates, two with Km values similar to those of lysosomal cathepsin B. In addition, the rates of inactivation of the sputum and lysosomal forms of the enzyme by L-3-carboxy-2,3-transepoxypropionyl-leucylamido(4-guanidino) butane (Compound E-64) were very similar. However, the sputum enzyme differed from lysosomal cathepsin B in the following respects. Inhibition by chicken cystatin was much weaker for sputum cathepsin B than for the lysosomal enzyme. Sputum cathepsin B had greater stability at pH 7.5 and a higher apparent Mr, even after deglycosylation, than lysosomal cathepsin B. We conclude that the form of cathepsin B found in sputum is probably a truncated form of human procathepsin B, with some differences in properties that could be of physiological importance.
authors.affiliation: Department of Biochemistry, Strangeways Research Laboratory, Cambridge, U.K.
authors.forename: D J
authors.initials: DJ
authors.lastname: Buttle
authors.forename: B C
authors.initials: BC
authors.lastname: Bonner
authors.forename: D
authors.initials: D
authors.lastname: Burnett
authors.forename: A J
authors.initials: AJ
authors.lastname: Barrett
mesh_terms: D001665:Binding Sites; D001987:Bronchiectasis / Q000201:enzymology*; D002401:Cathepsin B / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D011232:Chemical Precipitation; D002846:Chromatography, Affinity; D003978:Diazomethane / Q000031:analogs & derivatives; D004151:Dipeptides; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007122:Immunoelectrophoresis; D007700:Kinetics; D008970:Molecular Weight; D009844:Oligosaccharides / Q000032:analysis; D013183:Sputum / Q000201:enzymology*
chemical_list: D004151:Dipeptides; D009844:Oligosaccharides; C057752:benzyloxycarbonyltyrosylalanine diazomethane; D003978:Diazomethane; D002401:Cathepsin B