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Hexose metabolism in pancreatic islets: Succinate dehydrogenase activity in islet homogenates
Author(s) -
Rasschaert Joanne,
Malaisse Willy J.
Publication year - 1993
Publication title -
cell biochemistry and function
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 61
eISSN - 1099-0844
pISSN - 0263-6484
DOI - 10.1002/cbf.290110302
Subject(s) - fumarase , succinate dehydrogenase , biochemistry , dehydrogenase , nad+ kinase , enzyme , isocitrate dehydrogenase , citric acid cycle , branched chain alpha keto acid dehydrogenase complex , pancreatic islets , malate dehydrogenase , chemistry , islet , biology , endocrinology , insulin
Succinate dehydrogenase activity was measured in rat pancreatic islet homogenates incubated in the presence of [1,4‐ 14 C]succinate, the reaction velocity being judged through the generation of 14 CO 2 in the auxiliary reactions catalysed by pig heart fumarase and chicken liver NADP‐malate dehydrogenase. In the presence of 1·0 mM succinate, the reaction velocity averaged 5·53 ± 0·44 pmol min −1 μ g −1 islet protein. The K m for succinate was close to 0·4 mM and the enzymic activity was restricted to mitochondria. These kinetic results indicate that, under the present experimental conditions, the activity of succinate dehydrogenase does not vastly exceed that of either NAD‐isocitrate dehydrogenase or the 2‐ketoglutarate dehydrogenase complex, at least when the latter enzymes are activated by ADP and/or Ca 2+ . Nevertheless, the activity of succinate dehydrogenase is sufficient to account for the increase in O 2 uptake evoked in intact islets by the monomethyl ester of succinic acid. It could become a rate‐limiting step of the Krebs cycle in models of B‐cell dysfunction.