Measurement and modeling of glucose-6-phosphatase in pancreatic islets

被引:13
作者
Sweet, IR [1 ]
Najafi, H [1 ]
Li, GZ [1 ]
Grodberg, J [1 ]
Matschinsky, FM [1 ]
机构
[1] UNIV PENN, CTR DIABET RES, DEPT BIOCHEM, PHILADELPHIA, PA 19104 USA
来源
AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM | 1997年 / 272卷 / 04期
关键词
glucokinase; pancreatic beta-cells; oscillations; phosphofructokinase;
D O I
10.1152/ajpendo.1997.272.4.E696
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
In the beta-cells of the pancreas, glucose phosphorylation carried out by glucokinase is the rate-controlling step in glycolysis, and the kinetic characteristics of glucokinase govern to a high degree the dose-response relationship between glucose and insulin release. Because glucose-6-phosphatase (G-6-Pase) opposes the action of glucokinase, it may have a regulatory role in the release of insulin in response to glucose if the enzyme is present in the beta-cells. A number of researchers have reported finding high levels of G-6-Pase in islets, but quantitation of its activity remains controversial, mainly because of difficulties in solubilizing a particulate enzyme. Therefore a method developed to measure functional glucose phosphorylation activity in intact brain was applied (Chi, M. M.-Y., M. E. Pusateri, J. G. Carter, B. J. Norris, D. B. McDougal, Jr., and O. H. Lowry. Anal. Biochem. 161: 508-513, 1987), and the rates of accumulation and disappearance of 2-deoxyglucose 6-phosphate (DG-6-P) in freshly harvested islets were determined as a measure of glucose cycling. Islets were incubated in the presence of 30 mM 2-deoxyglucose (DG) for 60 min, and subsequently the incubation medium was replaced with medium containing no DG, but instead high levels of mannoheptulose as a blocker of phosphorylation. The content of DG-6-P in the islets was measured at strategic times during the protocol. As predicted by a mathematical model, DG-6-P accumulated in the presence of DG and decayed after its washout. Both of these results are consistent with islets containing dephosphorylation activity for this substrate. The kinetic curves were fit using a mathematical model, and the maximal G-6-Pase activity was estimated to be 0.13 +/- 0.005 mu mol . g(-1). min(-1). However, when the physiological effect of this amount of G-6-Pase activity was assessed by use of a model of glycolysis, it was found that the impact on glucose cycling and usage was insignificant. It was concluded that normal islets do contain measurable activity for dephosphorylating glucose 6-phosphate but that this enzymatic reaction does not play a role in glucose metabolism and sensing by the normal beta-cell.
引用
收藏
页码:E696 / E711
页数:16
相关论文
共 34 条
[1]  
ARION WJ, 1972, J BIOL CHEM, V247, P2558
[2]   GLUCOSE-6-PHOSPHATASE ACTIVITY OF MOUSE PANCREATIC ISLETS [J].
ASHCROFT, SJ ;
RANDLE, PJ .
NATURE, 1968, 219 (5156) :857-&
[3]   ENZYMES OF GLUCOSE METABOLISM IN NORMAL MOUSE PANCREATIC ISLETS [J].
ASHCROFT, SJ ;
RANDLE, PJ .
BIOCHEMICAL JOURNAL, 1970, 119 (01) :5-&
[4]   DISTRIBUTION ALONG RAT NEPHRON OF 3 ENZYMES OF GLUCONEOGENESIS IN ACIDOSIS AND STARVATION [J].
BURCH, HB ;
NARINS, RG ;
CHU, C ;
FAGIOLI, S ;
CHOI, S ;
MCCARTHY, W ;
LOWRY, OH .
AMERICAN JOURNAL OF PHYSIOLOGY, 1978, 235 (03) :F246-F253
[5]  
Burton K., 1968, Methods in Enzymology XIIB, V12, P163
[6]  
CANFIELD WK, 1988, J BIOL CHEM, V263, P7458
[7]   QUANTIFICATION OF GLUCOSE CYCLING AND THE EXTENT OF EQUILIBRATION OF GLUCOSE-6-PHOSPHATE WITH FRUCTOSE 6-PHOSPHATE IN ISLETS FROM OB/OB MICE [J].
CHANDRAMOULI, V ;
KHAN, A ;
OSTENSON, CG ;
BERGGREN, PO ;
LOW, H ;
LANDAU, BR ;
EFENDIC, SE .
BIOCHEMICAL JOURNAL, 1991, 278 :353-359
[8]   ENZYMATIC ASSAYS FOR 2-DEOXYGLUCOSE AND 2-DEOXYGLUCOSE 6-PHOSPHATE [J].
CHI, MMY ;
PUSATERI, ME ;
CARTER, JG ;
NORRIS, BJ ;
MCDOUGAL, DB ;
LOWRY, OH .
ANALYTICAL BIOCHEMISTRY, 1987, 161 (02) :508-513
[9]   Temporal sequence of metabolic and ionic events in glucose-stimulated clonal pancreatic beta-cells (HIT) [J].
Civelek, VN ;
Deeney, JT ;
Kubik, K ;
Schultz, V ;
Tornheim, K ;
Corkey, BE .
BIOCHEMICAL JOURNAL, 1996, 315 :1015-1019
[10]   HEXOSE METABOLISM IN PANCREATIC-ISLETS - ABSENCE OF GLUCOSE-6-PHOSPHATASE IN RAT ISLET CELLS [J].
GIROIX, MH ;
SENER, A ;
MALAISSE, WJ .
MOLECULAR AND CELLULAR ENDOCRINOLOGY, 1987, 49 (2-3) :219-225