Interaction of lysosomal cysteine proteinases with alpha 2-macroglobulin: conclusive evidence for the endopeptidase activities of cathepsins B and H.
The lysosomal cysteine proteinases, cathepsins B, H, and L, were all shown to bind to alpha 2-macroglobulin. The bound enzymes remained active against low-molecular-weight synthetic substrates and bound the active-site-directed inhibitor, benzyloxycarbonyl-125I-Tyr-Ala-diazomethane. Binding of the radiolabeled inhibitor to high-molecular-weight protein on sodium dodecyl sulfate polyacrylamide gels indicated that a proportion of the enzymes was covalently bound to alpha 2-macroglobulin. Cleavage fragments of alpha 2-macroglobulin of Mr 92,000 and 86,000 were seen for cathepsins B, H, and L, indicating cleavage in the bait region. Binding and cleavage were observed for both single-chain and two-chain forms of cathepsin B from human, ox, and pig livers, showing that all active forms of cathepsins B, H, and L are endopeptidases.
Mason
R W
RW
Department of Biochemistry, Strangeways Research Laboratory, Worts Causeway, Cambridge, United Kingdom.
D000818:Animals; D001345:Autoradiography; D002401:Cathepsin B / Q000378:metabolism*; D056655:Cathepsin H; D056668:Cathepsin L; D002403:Cathepsins / Q000378:metabolism*; D002417:Cattle; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism; D006801:Humans; D008247:Lysosomes / Q000201:enzymology*; D012756:Sheep; D013552:Swine; D000511:alpha-Macroglobulins / Q000378:metabolism*
D000511:alpha-Macroglobulins; D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; C534281:CTSL protein, human; D056668:Cathepsin L; C534126:CTSH protein, human; D056655:Cathepsin H