Molecular forms of cathepsin B in rat thyroid cells (FRTL5): comparison with molecular forms in liver (Hep G2) and insulin-secreting cells (HIT T15).
A radiolabelled peptide chloromethyl ketone (125I-tyrosyl-L-alanyl-L-lysyl-L-arginine chloromethyl ketone) was used to affinity-label proteinases in rat thyroid cells (FRTL5). Two major proteins of 34 kDa and 32 kDa were affinity-labelled. Inhibitor competition studies demonstrated that both proteins were cysteine proteinases. Over the range pH 5-8, they exhibited maximum activity against the affinity probe at pH 5. They were soluble rather than membrane-bound and were both glycosylated. The 32 kDa proteinase but not the 34 kDa proteinase was immunoprecipitated using an anti-rat liver cathepsin B antibody. The data suggested that these proteinases were molecular forms of cathepsin B. The affinity-labelled proteins in the thyroid were compared with those in an insulin-secreting cell line (HIT T15) and a liver cell line (Hep G2). Two molecular forms of cathepsin B of Mr 39,000 and 33,000 were identified in the insulin-secreting cell line and a single form of Mr 34,000 in the liver cell line. These molecular forms of cathepsin B may reflect the different functions and compartmentation of cathepsin B in these cells.
Docherty
K
K
Department of Medicine, University of Birmingham, Queen Elizabeth Hospital, U.K.
Phillips
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ID
D000818:Animals; D002401:Cathepsin B / Q000302:isolation & purification* / Q000378:metabolism; D002460:Cell Line; D006224:Cricetinae; D004848:Epithelium / Q000201:enzymology; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000201:enzymology; D007527:Isoenzymes / Q000302:isolation & purification* / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D008970:Molecular Weight; D051381:Rats; D013961:Thyroid Gland / Q000201:enzymology*
D007328:Insulin; D007527:Isoenzymes; D002401:Cathepsin B