title: Proteolytic and transhydrogenolytic activities in isolated pancreatic islets of rats.
abstract: In homogenates and subcellular fractions of pancreatic islets of Wistar rats we could demonstrate three groups of protein degrading enzymes. The proteinases of group 1 are characterized by both trypsin-like and carboxypeptidase B-like specificities with slightly acid pH optima (pH 5.5-6.5) and seem to play important roles in the conversion of proinsulin into insulin. The properties suggest that these enzymes localized in the secretion granule/mitochondria fraction are related to the tissue cathepsins. Group 2 enzymes are thiol-depending proteinases with a pH optimum at 7.0 occuring mainly in the cytosol and to a lesser extent in the fraction of nuclei and cell debris. Group 3 represents the thiol protein oxidoreductase with a pH optimum of 7.0. This enzyme degrading disulfide bonds could also be important in the formation of the disulfide bonds during protein folding after synthesis.
mesh_terms: D000818:Animals; D002268:Carboxypeptidases / Q000378:metabolism; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000201:enzymology*; D007700:Kinetics; D010088:Oxidoreductases / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D011490:Protein Disulfide Reductase (Glutathione) / Q000378:metabolism*; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology; D013379:Substrate Specificity; D014357:Trypsin / Q000378:metabolism
chemical_list: D010088:Oxidoreductases; D011490:Protein Disulfide Reductase (Glutathione); D002268:Carboxypeptidases; D010447:Peptide Hydrolases; D014357:Trypsin