PHOSPHOFRUCTOKINASE ISOZYMES IN PANCREATIC-ISLETS AND CLONAL BETA-CELLS (INS-1)

被引:73
作者
YANEY, GC
SCHULTZ, V
CUNNINGHAM, BA
DUNAWAY, GA
CORKEY, BE
TORNHEIM, K
机构
[1] BOSTON UNIV,SCH MED,EVANS DEPT MED,DEPT BIOCHEM,DIABET & METAB UNIT,BOSTON,MA 02118
[2] SO ILLINOIS UNIV,SCH MED,DEPT PHARMACOL,SPRINGFIELD,IL 62794
关键词
D O I
10.2337/diabetes.44.11.1285
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
Normal insulin secretion is oscillatory in vivo, and the oscillations are impaired in type II diabetes, We and others have shown oscillations in insulin secretion from isolated perifused islets stimulated with glucose, and in this study we show oscillations in insulin secretion from the glucose-sensitive clonal beta-cell line INS-1, We have proposed that the oscillatory insulin secretion may be caused by spontaneous oscillations of glycolysis and the ATP:ADP ratio in the beta-cell, analogous to those seen in glycolyzing muscle extracts, The mechanism of the latter involves autocatalytic activation of the key regulatory enzyme, phosphofructokinase (PFK), by its product fructose 1,6-bisphosphate (F16BP), However, of the three PFK subunit isoforms (M- [muscle], L- [liver], and C-type, predominant in fibroblasts), only M-type is activated by micromolar F16BP at near-physiological conditions, We therefore studied PFK isoforms in the beta-cell, Western analysis of PFK subunits in isolated rat islets and INS-1 cells showed the presence of M-type, as well as C-type and perhaps lesser amounts of L-type, Kinetic studies of PFK activity in INS-I cell extracts showed strong activation by micromolar concentrations of F16BP at near-physiological concentrations of ATP (several millimolar) and AMP and fructose 6-phosphate (micromolar), indicative of the M-type isoform, Activation by submicromolar concentrations of fructose 2,6-bisphosphate (F26BP) and potent inhibition by citrate were also observed, The F16BP-stimulatable activity was about one-half of the F26BP-stimulatable activity, These experiments demonstrate that beta-cells contain tire M-type isoform of PFK with the requisite regulatory properties for generating glycolytic oscillations that may be the basis of oscillatory insulin secretion.
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页码:1285 / 1289
页数:5
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