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Enzymes of glucose metabolism in normal mouse pancreatic islets.
Biochem J. 1970 Aug; 119(1):5-15.BJ

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 K(m) 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 K(m) 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 K(m) 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 K(m) values of 2.5 and 21mum for NADP(+) and 6-phosphogluconate respectively. 5. Glucose 6-phosphate dehydrogenase had K(m) values of 4 and 22mum for NADP(+) and glucose 6-phosphate. The K(m) 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 beta-cell glucoreceptor mechanism.

Authors

No affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

4395001

Citation

Ashcroft, S J., and P J. Randle. "Enzymes of Glucose Metabolism in Normal Mouse Pancreatic Islets." The Biochemical Journal, vol. 119, no. 1, 1970, pp. 5-15.
Ashcroft SJ, Randle PJ. Enzymes of glucose metabolism in normal mouse pancreatic islets. Biochem J. 1970;119(1):5-15.
Ashcroft, S. J., & Randle, P. J. (1970). Enzymes of glucose metabolism in normal mouse pancreatic islets. The Biochemical Journal, 119(1), 5-15.
Ashcroft SJ, Randle PJ. Enzymes of Glucose Metabolism in Normal Mouse Pancreatic Islets. Biochem J. 1970;119(1):5-15. PubMed PMID: 4395001.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Enzymes of glucose metabolism in normal mouse pancreatic islets. AU - Ashcroft,S J, AU - Randle,P J, PY - 1970/8/1/pubmed PY - 1970/8/1/medline PY - 1970/8/1/entrez SP - 5 EP - 15 JF - The Biochemical journal JO - Biochem. J. VL - 119 IS - 1 N2 - 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 K(m) 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 K(m) 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 K(m) 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 K(m) values of 2.5 and 21mum for NADP(+) and 6-phosphogluconate respectively. 5. Glucose 6-phosphate dehydrogenase had K(m) values of 4 and 22mum for NADP(+) and glucose 6-phosphate. The K(m) 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 beta-cell glucoreceptor mechanism. SN - 0264-6021 UR - https://www.unboundmedicine.com/medline/citation/4395001/Enzymes_of_glucose_metabolism_in_normal_mouse_pancreatic_islets_ L2 - https://portlandpress.com/biochemj/article-lookup/doi/10.1042/bj1190005 DB - PRIME DP - Unbound Medicine ER -