Skip to main content
PMC home page
Biochemical Journal logoLink to Biochemical Journal
. 1970 Aug;119(1):5–15. doi: 10.1042/bj1190005

Enzymes of glucose metabolism in normal mouse pancreatic islets

S J H Ashcroft 1, P J Randle 1
PMCID: PMC1179311  PMID: 4395001

Abstract

1. Glucose-phosphorylating and glucose 6-phosphatase activities, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, NADP+-linked isocitrate dehydrogenase, `malic' enzyme and pyruvate carboxylase were assayed in homogenates of normal mouse islets. 2. Two glucose-phosphorylating activities were detected; the major activity had Km 0.075mm for glucose and was inhibited by glucose 6-phosphate (non-competitive with glucose) and mannoheptulose (competitive with glucose). The other (minor) activity had a high Km for glucose (mean value 16mm) and was apparently not inhibited by glucose 6-phosphate. 3. Glucose 6-phosphatase activity was present in amounts comparable with the total glucose-phosphorylating activity, with Km 1mm for glucose 6-phosphate. Glucose was an inhibitor and the inhibition showed mixed kinetics. No inhibition of glucose 6-phosphate hydrolysis was observed with mannose, citrate or tolbutamide. The inhibition by glucose was not reversed by mannoheptulose. 4. 6-Phosphogluconate dehydrogenase had Km values of 2.5 and 21μm for NADP+ and 6-phosphogluconate respectively. 5. Glucose 6-phosphate dehydrogenase had Km values of 4 and 22μm for NADP+ and glucose 6-phosphate. The Km for glucose 6-phosphate was considerably below the intra-islet concentration of glucose 6-phosphate at physiological extracellular glucose concentrations. The enzyme had no apparent requirement for cations. Of a number of possible modifiers of glucose 6-phosphate dehydrogenase, only NADPH was inhibitory. The inhibition by NADPH was competitive with NADP+ and apparently mixed with respect to glucose 6-phosphate. 6. NADP+–isocitrate dehydrogenase was present but the islet homogenate contained little, if any, `malic' enzyme. The presence of pyruvate carboxylase was also demonstrated. 7. The results obtained are discussed with reference to glucose phosphorylation and glucose 6-phosphate oxidation in the intact mouse islet, and the possible nature of the β-cell glucoreceptor mechanism.

Full text

PDF
5

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Ashcroft S. J., Hedeskov C. J., Randle P. J. Glucose metabolism in mouse pancreatic islets. Biochem J. 1970 Jun;118(1):143–154. doi: 10.1042/bj1180143. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Ashcroft S. J., Randle P. J. Glucose phosphorylation in mouse pancreatic islets. Biochem J. 1968 Apr;107(4):599–600. doi: 10.1042/bj1070599. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Ashcroft S. J., Randle P. J. Glucose-6-phosphatase activity of mouse pancreatic islets. Nature. 1968 Aug 24;219(5156):857–858. doi: 10.1038/219857a0. [DOI] [PubMed] [Google Scholar]
  4. Coll-Garcia E., Gill J. R. Insulin release by isolated pancreatic islets of the mouse incubated in vitro. Diabetologia. 1969 Apr;5(2):61–66. doi: 10.1007/BF01211999. [DOI] [PubMed] [Google Scholar]
  5. Coore H. G., Randle P. J. Regulation of insulin secretion studied with pieces of rabbit pancreas incubated in vitro. Biochem J. 1964 Oct;93(1):66–78. doi: 10.1042/bj0930066. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Flint A. P., Denton R. M. The role of nicotinamide-adenine dinucleotide phosphate-dependent malate dehydrogenase and isocitrate dehydrogenase in the supply of reduced nicotinamide-adenine dinucleotide phosphate for steroidogenesis in the superovulated rat ovary. Biochem J. 1970 Mar;117(1):73–83. doi: 10.1042/bj1170073. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. GLASER L., BROWN D. H. Purification and properties of d-glucose-6-phosphate dehydrogenase. J Biol Chem. 1955 Sep;216(1):67–79. [PubMed] [Google Scholar]
  8. LAZARUS S. S. Acid and glucose-6-phosphatase activity of pancreatic B cells after cortisone and sulfonylureas. Proc Soc Exp Biol Med. 1959 Nov;102:303–306. doi: 10.3181/00379727-102-25227. [DOI] [PubMed] [Google Scholar]
  9. Malaisse W. J., Lea M. A., Malaisse-Lagae F. The effect of mannoheptulose on the phosphorylation of glucose and the secretion of insulin by islets of Langerhans. Metabolism. 1968 Feb;17(2):126–132. doi: 10.1016/0026-0495(68)90138-8. [DOI] [PubMed] [Google Scholar]
  10. Matschinsky F. M., Ellerman J. E. Metabolism of glucose in the islets of Langerhans. J Biol Chem. 1968 May 25;243(10):2730–2736. [PubMed] [Google Scholar]
  11. Matschinsky F. M., Kauffman F. C., Ellerman J. E. Effect of hyperglycemia on the hexose monophosphate shunt in islets of Langerhans. Diabetes. 1968 Aug;17(8):475–480. doi: 10.2337/diab.17.8.475. [DOI] [PubMed] [Google Scholar]
  12. Matschinsky F. M., Rutherford C. R., Ellerman J. E. Accumulation of citrate in pancreatic islets of obese hyperglycemic mice. Biochem Biophys Res Commun. 1968 Dec 9;33(5):855–862. doi: 10.1016/0006-291x(68)90240-4. [DOI] [PubMed] [Google Scholar]
  13. Moellering H., Gruber W. Determination of citrate with citrate lyase. Anal Biochem. 1966 Dec;17(3):369–376. doi: 10.1016/0003-2697(66)90172-2. [DOI] [PubMed] [Google Scholar]
  14. Montague W., Taylor K. W. Pentitols and insulin release by isolated rat islets of Langerhans. Biochem J. 1968 Sep;109(3):333–339. doi: 10.1042/bj1090333. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Montague W., Taylor K. W. Regulation of insulin secretion by short chain fatty acids. Nature. 1968 Mar 2;217(5131):853–853. doi: 10.1038/217853a0. [DOI] [PubMed] [Google Scholar]
  16. Nordlie R. C., Lygre D. G. The inhibition by citrate of inorganic pyrophosphate-glucose phosphotransferase and glucose 6-phosphatase. J Biol Chem. 1966 Jul 10;241(13):3136–3141. [PubMed] [Google Scholar]
  17. Ockerman P. A. Glucose-6-phosphatase assay on microgram amounts of liver tissue. Clin Chim Acta. 1967 Aug;17(2):201–206. doi: 10.1016/0009-8981(67)90119-2. [DOI] [PubMed] [Google Scholar]
  18. TäljedalIB Presence, induction and possible role of glucose 6-phosphatase in mammalian pancreatic islets. Biochem J. 1969 Sep;114(2):387–394. doi: 10.1042/bj1140387. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Veech R. L., Eggleston L. V., Krebs H. A. The redox state of free nicotinamide-adenine dinucleotide phosphate in the cytoplasm of rat liver. Biochem J. 1969 Dec;115(4):609–619. doi: 10.1042/bj1150609a. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Biochemical Journal are provided here courtesy of The Biochemical Society

RESOURCES