The stimulus-secretion coupling of glucose-induced insulin release: Enzymes of mannose metabolism in pancreatic islets

Anjaneyulu, Renu; Kowluru, Anjaneyulu; Carpinelli, Ângelo Rafael; Sener, Abdullah; Malaisse, Willy

doi:10.1016/0003-9861(81)90342-8

Cited by 17 publications

(9 citation statements)

References 26 publications

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“…Half-maximal saturation of glucokinase by mannose occurs at 11-13 mM with a-mannose as substrate (Table 1). By comparison, the S 05 value for pmannose is 17-20 mM and an intermediate value of [13][14][15] mM is observed with a,p-mannose. The Michaelis-Menten constants determined from the linear portion of Hanes-Woolf plots show a similar ordered sequence with a-mannose < a,p-mannose < p-mannose for glucokinase preparations from liver or insulinomas (Table 1).…”

Section: Resultsmentioning

confidence: 91%

Mannose Phosphorylation by Glucokinase from Liver and Transplantable Insulinoma: Cooperativity and Discrimination of Anomers

Meglasson¹,

Schinco²,

Matschinsky³

1983

Diabetes

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Glucokinase from rat liver or transplantable, radiation-induced insulinomas was partially purified by ion exchange chromatography using DEAE-Cibacron Blue F3GA agarose. Phosphorylation of alpha,beta-D-mannose by glucokinase occurred with cooperative rate dependence on mannose concentration (nH: 1.50). Half-maximal phosphorylation rate occurred at 14 mM alpha,beta-D-mannose. The alpha- and beta-anomers of mannose were phosphorylated with sigmoidal kinetics (nH: 1.57 and 1.42, respectively). The affinity of glucokinase for alpha-D-mannose is higher than for beta-D-mannose (S0.5: 12 mM versus 19 mM). The maximum phosphorylation rate is slightly higher, about 10%, with beta-D-mannose than with alpha-D-mannose. Islet glucokinase has previously been shown to be chromatographically and kinetically identical to glucokinase from insulinoma and liver; therefore, evidence that glucokinase from these two tissues phosphorylates mannose with cooperative rate dependence and differentiates mannose anomers supports the glucokinase-glucose sensor hypothesis.

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Section: Resultsmentioning

confidence: 91%

Mannose Phosphorylation by Glucokinase from Liver and Transplantable Insulinoma: Cooperativity and Discrimination of Anomers

Meglasson¹,

Schinco²,

Matschinsky³

1983

Diabetes

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“…We interpreted these findings as indicating that the embryotoxicity of mannose is linked to its intracellular metabolism and that this metabolism is delimited by competitions between mannose and glucose for phosphorylation via hexokinases that do not distinguish between the two hexoses in most tissues (3,6,11,21,22) [including the 10-and 11-day-old rat conceptus (Passonneau, J., and N. Freinkel, unpublished observations)]. In the present studies, plasma mannose levels did not exceed 3% of the concurrent glucose concentration in any instance, and the percentages were only minimally increased after an overnight fast in the women with diabetes mellitus.…”

Section: Discussionmentioning

confidence: 99%

“…Table 1 summarizes pertinent details concerning the study populations, mean (±SE) values for plasma and amniotic fluid glucose and mannose in each group, and the range of values for each parameter. Since hexokinase reacts with mannose almost as effectively as with glucose in most tissues (3,6,11,21,22), the mannose values are also expressed as a percentage of the concurrent values for glucose (percentage of glucose) to describe the competitive potentialities. Values are the mean ± SE; the range is in parentheses.…”

Section: Analytical Techniquesmentioning

confidence: 99%

“…However, since mannose did not exceed 3% of the concurrent concentration of glucose in any instance, it does not seem likely that endogenous levels of circulating mannose can modify glucose utilization appreciably by competing with glucose for phosphorylation via hexokinase and subsequent intracellular processing. (J Clin Endocrinol Metab 62: 984,1986) A LTHOUGH D-mannose, the epimer of D-glucose, can L stimulate insulin secretion in pancreatic islets ( 1 -3) and replace glucose in a variety of glucose-transporting and glucose-metabolizing systems (3)(4)(5)(6)(7)(8), relatively few measurements of plasma mannose concentrations have been reported (9,10). The paucity of data has been due in part to the lack of a simple and specific analytical technique for estimating mannose in the presence of marked glucose excess, as well as the suspicion that plasma mannose may be low and comparatively unaffected by dietary perturbations in view of the poor absorption of mannose from the gastrointestinal tract (11, MANNOSE AND GLUCOSE IN LATE PREGNANCY 985 and venous plasma were obtained after an overnight fast during weeks 34-40 of gestation in 31 pregnant women with diabetes mellitus (fasting) and 3-4 h after breakfast in an additional 19 patients (nonfasting).…”

mentioning

confidence: 99%

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Relationships between Glucose and Mannose during Late Gestation in Normal Pregnancy and Pregnancy Complicated by Diabetes Mellitus: Concurrent Concentrations in Maternal Plasma and Amniotic Fluid†

Akazawa

Metzger

Freinkel

1986

The Journal of Clinical Endocrinology & Metabolism

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Enzymatic assays were modified to permit sensitive and highly reproducible simultaneous measurements of D-mannose and D-glucose in biological fluids during weeks 34-40 of human pregnancy. Plasma mannose and glucose averaged 9.8 +/- 0.4 (+/- SEM) and 790 +/- 16 micrograms/ml, respectively, after an overnight fast in pregnant women (n = 22) with normal carbohydrate metabolism. Significantly higher plasma mannose levels were found, despite only minor increases in plasma glucose, in pregnant women with relatively well controlled diabetes mellitus after an overnight fast (16.9 +/- 0.6 micrograms/ml mannose; 883 +/- 29 micrograms/ml glucose; n = 31) or 3-4 h after breakfast (15.7 +/- 1.2 micrograms/ml mannose; 1159 +/- 101 micrograms/ml glucose; n = 19). Plasma mannose correlated significantly with plasma glucose in the women with diabetes mellitus, particularly after an overnight fast. Samples of amniotic fluid were also obtained from the gravida with diabetes mellitus to provide some index of simultaneous relationships in utero. Amniotic fluid mannose and glucose averaged 5.9 +/- 0.4 and 302 +/- 24 micrograms/ml, respectively, after an overnight fast and 6.7 +/- 1.3 and 459 +/- 84 micrograms/ml 3-4 h after breakfast. In amniotic fluid, as in plasma, the concurrent levels of mannose and glucose conformed to relatively fixed relationships. Thus, both fetus and mother appear to be exposed to readily demonstrable amounts of mannose during late gestation and the absolute as well as relative abundance of mannose may be increased coincident with faulty maternal glucoregulation. However, since mannose did not exceed 3% of the concurrent concentration of glucose in any instance, it does not seem likely that endogenous levels of circulating mannose can modify glucose utilization appreciably by competing with glucose for phosphorylation via hexokinase and subsequent intracellular processing.

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“…Estimates depend on the assumption that before each molecule of glucose 6-P is hydrolysed to glucose, because of rapid equilibration between glucose 6-P and fructose 6-P, a hydrogen from the medium is bound to carbon 2 of the glucose 6-P. Rapid equilibration of glucose 6-P with fructose 6-P is expected because of a relatively high activity of phosphohexose isomerase in islets [24]. Isotopic equilibration in human liver was estimated to reach 80±92 % [25].…”

Section: Methodsmentioning

confidence: 99%

Increased glucocorticoid sensitivity in islet beta-cells: effects on glucose 6-phosphatase, glucose cycling and insulin release

et al. 1998

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Glucose-6-phosphatase (G6Pase) and glucokinase activities can be demonstrated in pancreatic islets from mammalian species [1±4]. Glucokinase appears to be the rate limiting enzyme of glycolysis in the beta-cell, regulating the dose-response relationship between glucose utilization and insulin release [4]. Since G6Pase opposes the action of glucokinase, a possible role for G6Pase in the metabolic regulation of insulin release was postulated [2,3]. There are several reports of relatively low G6Pase activity in homogenates of normal mammalian islets [1±4], one of activity exceeding that in liver [5] and one of no activity [6]. We found low activity in permeabilized and sonicated islets from normal rats and mice [7]. Sweet et al. [8] also found low G6Pase activity in intact islets from normal rats.Glucose cycling is the simultaneous phosphorylation of glucose to glucose-6-P and dephosphorylation of glucose-6-P to glucose with the resulting consumption of ATP [9]. In accordance with reports of low G6Pase activity, we demonstrated a low rate of glucose cycling in intact islets from normal mice, dephosphorylation occurring at only 3 % of the rate of phosphorylation [10]. However, in islets from ob/ob mice, 30±40 % of phosphorylated glucose was dephosphorylated [10]. Glucose cycling was also increased in islets from other animal models of Type II diabetes [11,12]. In accordance with these results, G6Pase activity was several fold higher in islets from diabetic than normal animals [7,13] and islet G6Pase gene expression was increased during the development of diabetes in Zucker rats [14]. Diabetologia (1998) Summary Glucose-6-phosphatase (G6Pase) activity and the rate of glucose cycling are increased in islets from animal models of Type II (non-insulin-dependent) diabetes mellitus. Glucocorticoid treatment further stimulates these processes and inhibits glucose-induced insulin release. To determine whether these effects result from a direct action of glucocorticoids on the beta-cells, we used isolated islets. The islets were from transgenic mice overexpressing the glucocorticoid receptor in their beta-cells to increase the cells' sensitivity to glucocorticoid. Islets from transgenic and non-transgenic control mice utilized and oxidized the same amount of glucose. In contrast, islet G6Pase activity was 70 % higher, glucose cycling was increased threefold and insulin release was 30 % lower in islets from transgenic mice. Hepatic G6Pase activity was the same in transgenic and control mice. Dexamethasone administration increased G6Pase activity and glucose cycling and decreased insulin release in both transgenic and control mouse islets. We conclude that glucocorticoids stimulate islet G6Pase activity and glucose cycling by acting directly on the beta-cell. That activity may be linked to the inhibition of insulin release. [Diabetologia (1998) 41: 634±639]

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The stimulus-secretion coupling of glucose-induced insulin release: Enzymes of mannose metabolism in pancreatic islets

Cited by 17 publications

References 26 publications

Mannose Phosphorylation by Glucokinase from Liver and Transplantable Insulinoma: Cooperativity and Discrimination of Anomers

Mannose Phosphorylation by Glucokinase from Liver and Transplantable Insulinoma: Cooperativity and Discrimination of Anomers

Relationships between Glucose and Mannose during Late Gestation in Normal Pregnancy and Pregnancy Complicated by Diabetes Mellitus: Concurrent Concentrations in Maternal Plasma and Amniotic Fluid†

Increased glucocorticoid sensitivity in islet beta-cells: effects on glucose 6-phosphatase, glucose cycling and insulin release

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