Polyhydroxybenzoates inhibit ascorbic acid activation of mitochondrial glycerol-3-phosphate dehydrogenase: implications for glucose metabolism and insulin secretion.
Glycerol-3-phosphate dehydrogenase from pig brain mitochondria was stimulated 2.2-fold by the addition of 50 microm l-ascorbic acid. Enzyme activity, dependent upon the presence of l-ascorbic acid, was inhibited by lauryl gallate, propyl gallate, protocatechuic acid ethyl ester, and salicylhydroxamic acid. Homogeneous pig brain mitochondrial glycerol-3-phosphate dehydrogenase was activated by either 150 microm L-ascorbic acid (56%) or 300 microm iron (Fe(2+) or Fe(3+) (62%)) and 2.6-fold by the addition of both L-ascorbic acid and iron. The addition of L-ascorbic acid and iron resulted in a significant increase of k(cat) from 21.1 to 64.1 s(-1), without significantly increasing the K(m) of L-glycerol-3-phosphate (10.0-14.5 mm). The activation of pure glycerol-3-phosphate dehydrogenase by either L-ascorbic acid or iron or its combination could be totally inhibited by 200 microm propyl gallate. The metabolism of [5-(3)H]glucose and the glucose-stimulated insulin secretion from rat insulinoma cells, INS-1, were effectively inhibited by 500 microm or 1 mm propyl gallate and to a lesser extent by 5 mm aminooxyacetate, a potent malate-aspartate shuttle inhibitor. The combined data support the conclusion that l-ascorbic acid is a physiological activator of mitochondrial glycerol-3-phosphate dehydrogenase, that the enzyme is potently inhibited by agents that specifically inhibit certain classes of di-iron metalloenzymes, and that the enzyme is chiefly responsible for the proximal signal events in INS-1 cell glucose-stimulated insulin release.
Wells
W W
WW
Department of Biochemistry and the Department of Physiology, Michigan State University, East Lansing 48824, USA.
Xu
D P
DP
Washburn
M P
MP
Cirrito
H K
HK
Olson
L K
LK
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D005947:Glucose / Q000378:metabolism; D005993:Glycerolphosphate Dehydrogenase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D062385:Hydroxybenzoates / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007501:Iron / Q000037:antagonists & inhibitors / Q000494:pharmacology; D007515:Islets of Langerhans / Q000378:metabolism / Q000473:pathology; D008667:Metalloproteins / Q000037:antagonists & inhibitors; D008928:Mitochondria / Q000201:enzymology*; D011435:Propyl Gallate / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction; D013552:Swine; D013687:Telencephalon
D062385:Hydroxybenzoates; D007328:Insulin; D008667:Metalloproteins; D011435:Propyl Gallate; D007501:Iron; D005993:Glycerolphosphate Dehydrogenase; D005947:Glucose; D001205:Ascorbic Acid