title: Cathepsin B-related proteases in the insulin secretory granule.
abstract: The distribution of proteases potentially reactive with peptide sequences containing pairs of basic amino acids or single basic amino acids was studied in subcellular fractions of a transplantable rat insulinoma using the affinity probes 125I-Tyr-Ala-Lys- ArgCH2Cl and 125I-Tyr-Ala-norleucine- ArgCH2Cl . Both probes labeled predominantly proteins of Mr = 39,000, 31,500, and 25,000. The Mr = 25,000 component appeared to be of lysosomal origin, while the Mr = 39,000 and 31,500 proteins were present in both the lysosomes and insulin granules. The Mr = 39,000 and 31,500 proteins were identified as precursor/product forms of the cysteine protease cathepsin B, while assays performed with fluorigenic peptide substrates suggested that the Mr = 25,000 protein was probably cathepsin L and/or H. The greater reactivity of the Mr = 39,000 form with the dibasic probe suggests that the relative proportions of the Mr = 39,000 and 31,500 forms of cathepsin B in different organelles may determine the extent to which the enzyme expresses activity as a specific (prohormone processing) endopeptidase or a more general (degradative) peptidase.
mesh_terms: D007516:Adenoma, Islet Cell / Q000201:enzymology*; D000818:Animals; D002401:Cathepsin B; D002403:Cathepsins / Q000302:isolation & purification / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000201:enzymology* / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000201:enzymology* / Q000378:metabolism; D008970:Molecular Weight; D010190:Pancreatic Neoplasms / Q000201:enzymology* / Q000378:metabolism; D010434:Pepsin A; D051381:Rats
chemical_list: D007328:Insulin; D002403:Cathepsins; D002401:Cathepsin B; D010434:Pepsin A