Relevance of lactate dehydrogenase activity to the control of oxidative glycolysis in pancreatic islet B-cells.
The activities of hexokinase isoenzymes, lactate dehydrogenase, cytosolic NAD-linked glycerophosphate dehydrogenase, mitochondrial FAD-linked glycerophosphate dehydrogenase, and glutamate dehydrogenase were measured in homogenates of rat purified pancreatic B and non-B islet cells. In B cell homogenates, the maximal activity of hexokinase and glucokinase was one to two orders of magnitude lower than that of lactate dehydrogenase. The activity of the mitochondrial FAD-linked glycerophosphate dehydrogenase was also much lower than that of the cytosolic NAD-linked glycerophosphate dehydrogenase . A comparable hierarchy in the activity of these enzymes was observed in non-B islet cells. These findings reinforce the view that the preferential stimulation of oxidative glycolysis observed in insulin-producing cells, when exposed to high concentrations of D-glucose, is attributable to a Ca2+-induced activation of the mitochondrial FAD-linked glycerophosphate dehydrogenase, rather than to saturation of the catalytic activity of lactate dehydrogenase.
Jijakli
H
H
Laboratory of Experimental Medicine, Brussels Free University, Belgium.
Rasschaert
J
J
Nadi
A B
AB
Leclercq-Meyer
V
V
Sener
A
A
Malaisse
W J
WJ
D000818:Animals; D002469:Cell Separation; D003600:Cytosol / Q000201:enzymology; D005934:Glucagon / Q000032:analysis / Q000378:metabolism; D005941:Glucokinase / Q000378:metabolism; D005969:Glutamate Dehydrogenase / Q000378:metabolism; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D006019:Glycolysis; D006593:Hexokinase / Q000378:metabolism*; D007328:Insulin / Q000032:analysis / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology* / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology; D010084:Oxidation-Reduction; D051381:Rats
D007328:Insulin; D007527:Isoenzymes; D005934:Glucagon; D005993:Glycerolphosphate Dehydrogenase; D007770:L-Lactate Dehydrogenase; D005969:Glutamate Dehydrogenase; D006593:Hexokinase; D005941:Glucokinase