A model of the Drosophila melanogaster glycerol-3-phosphate oxidase-encoding gene

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.

Structural organization and mapping of the human mitochondrial glycerol phosphate dehydrogenase-encoding gene and pseudogene

Mitochondrial glycerol phosphate dehydrogenase (mtGPD) is the rate-limiting enzyme in the glycerol phosphate shuttle, which is thought to play an important role in cells that require an active glycolytic pathway. Abnormalities in mtGPD have been proposed as a potential cause for non-insulin-dependent diabetes mellitus. To facilitate genetic studies, we have isolated genomic clones containing the coding regions of the human mtGPD-encoding gene (GPDM). The gene contains 17 exons and is estimated to span more than 80 kb. All splice junctions contain GT/AG consensus sequences. Introns interrupt the sequences encoding the leader peptide, the FAD-binding site, the calcium-binding regions, and a conserved central element postulated to play a role in glycerol phosphate binding. Fluorescence in situ hybridization was used to map this gene to chromosome 2, band q24.1. A retropseudogene was identified and mapped to chromosome 17.