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  • Title: Proteolytic and transhydrogenolytic activities in isolated pancreatic islets of rats.
    Author: Zühlke H, Kohnert KD, Jahr H, Schmidt S, Kirschke H, Steiner DF.
    Journal: Acta Biol Med Ger; 1977; 36(11-12):1695-703. PubMed ID: 358709.
    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.
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