RELEVANCE OF LACTATE-DEHYDROGENASE ACTIVITY TO THE CONTROL OF OXIDATIVE GLYCOLYSIS IN PANCREATIC-ISLET B-CELLS

The activities of hexokinase isoenzymes, lactate dehydrogenase, cytoso lic NAD-linked glycerophosphate dehydrogenase, mitochondrial FAD-linke d glycerophosphate dehydrogenase, and glutamate dehydrogenase were mea sured in homogenates of rat purified pancreatic B and non-B islet cell s, In B cell homogenates, the maximal activity of hexokinase and gluco kinase was one to two orders of magnitude lower than that of lactate d ehydrogenase. The activity of the mitochondrial FAD-linked glycerophos phate 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 fin dings reinforce the view that the preferential stimulation of oxidativ e glycolysis observed in insulin-producing cells, when exposed to high concentrations of D-glucose, is attributable to a Ca2+-induced activa tion of the mitochondrial FAD-linked glycerophosphate dehydrogenase, r ather than to saturation of the catalytic activity of lactate dehydrog enase. (C) 1996 Academic Press, Inc.