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.
Research Article| September 15 1988
A catalytically active high-Mr form of human cathepsin B from sputum
D J Buttle;
B C Bonner;
Biochem J (1988) 254 (3): 693–699.
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D J Buttle, B C Bonner, D Burnett, A J Barrett; A catalytically active high-Mr form of human cathepsin B from sputum. Biochem J 15 September 1988; 254 (3): 693–699. doi: https://doi.org/10.1042/bj2540693
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