title: Evidence that adrenal hexose-6-phosphate dehydrogenase can effect microsomal P450 cytochrome steroidogenic enzymes.
abstract: The role of adrenal hexose-6-phosphate dehydrogenase in providing reducing equivalents to P450 cytochrome steroidogenic enzymes in the endoplasmic reticulum is uncertain. Hexose-6-phosphate dehydrogenase resides in the endoplasmic reticulum lumen and co-localizes with the bidirectional enzyme 11β-hydroxysteroid dehydrogenase 1. Hexose-6-phosphate dehydrogenase likely provides 11β-hydroxysteroid dehydrogenase 1 with NADPH electrons via channeling. Intracellularly, two compartmentalized reactions generate NADPH upon oxidation of glucose-6-phosphate: cytosolic glucose-6-phosphate dehydrogenase and microsomal hexose-6-phosphate dehydrogenase. Because some endoplasmic reticulum enzymes require an electron donor (NADPH), it is conceivable that hexose-6-phosphate dehydrogenase serves in this capacity for these pathways. Besides 11β-hydroxysteroid dehydrogenase 1, we examined whether hexose-6-phosphate dehydrogenase generates reduced pyridine nucleotide for pivotal adrenal microsomal P450 enzymes. 21-hydroxylase activity was increased with glucose-6-phosphate and, also, glucose and glucosamine-6-phosphate. The latter two substrates are only metabolized by hexose-6-phosphate dehydrogenase, indicating that requisite NADPH for 21-hydroxylase activity was not via glucose-6-phosphate dehydrogenase. Moreover, dihydroepiandrostenedione, a non-competitive inhibitor of glucose-6-phosphate dehydrogenase, but not hexose-6-phosphate dehydrogenase, did not curtail activation by glucose-6-phosphate. Finally, the most compelling observation was that the microsomal glucose-6-phosphate transport inhibitor, chlorogenic acid, blunted the activation by glucose-6-phosphate of both 21-hydroxylase and 17-hydroxylase indicating that luminal hexose-6-phosphate dehydrogenase can supply NADPH for these enzymes. Analogous kinetic observations were found with microsomal 17-hydroxylase. These findings indicate that hexose-6-phosphate dehydrogenase can be a source, but not exclusively so, of NADPH for several adrenal P450 enzymes in the steroid pathway. Although the reduced pyridine nucleotides are produced intra-luminally, these compounds may also slowly transverse the endoplasmic reticulum membrane by unknown mechanisms.
authors.affiliation: University of Alabama at Birmingham, Department of Pediatrics, Endocrinology, USA.
authors.forename: Christy A
authors.initials: CA
authors.lastname: Foster
authors.forename: Gail J
authors.initials: GJ
authors.lastname: Mick
authors.forename: Xudong
authors.initials: X
authors.lastname: Wang
authors.forename: Kenneth
authors.initials: K
authors.lastname: McCormick
mesh_terms: D043205:11-beta-Hydroxysteroid Dehydrogenase Type 1 / Q000378:metabolism*; D000311:Adrenal Glands / Q000201:enzymology*; D000818:Animals; D002237:Carbohydrate Dehydrogenases / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005944:Glucosamine / Q000031:analogs & derivatives / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D008861:Microsomes / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism*; D013255:Steroid 21-Hydroxylase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013552:Swine
chemical_list: D004791:Enzyme Inhibitors; C001293:glucosamine 6-phosphate; D009249:NADP; D019298:Glucose-6-Phosphate; D002237:Carbohydrate Dehydrogenases; C020552:galactose-6-phosphate dehydrogenase; D043205:11-beta-Hydroxysteroid Dehydrogenase Type 1; D013255:Steroid 21-Hydroxylase; D013254:Steroid 17-alpha-Hydroxylase; D005947:Glucose; D005944:Glucosamine