title: Isopentenoid synthesis in isolated embryonic Drosophila cells. Possible regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity by shunted mevalonate carbon.
abstract: Our previous studies (Watson, J. A., Havel, C. M., Lobos, D. V., Baker, F. C., and Morrow, C. J. (1985) J. Biol. Chem. 260, 14083-14091) suggested that a matabolite, distal to isopentenyl 1-pyrophospate (IPP), served as a regulatory signal for sterol-independent modulation of Kc cell 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity. This report summarizes efforts to localize the potential source of the post-IPP regulatory signal molecule. We found no direct correlation between mevalonate-mediated suppression of Kc cell HMG-CoA reductase activity and the rates of [1-14C]-, [3-14C]-, [5-14C]-, or [5-3H]mevalonate incorporation into either carbon dioxide, neutral lipids, water, or water-soluble isopentenoid pyrophosphate esters. [1-14C]Mevalonate's rate of conversion to 14CO2 (a measure of total isopentenyl 1-pyrophosphate synthesis) was minimally 5-fold greater than that for neutral isopentenoid lipid synthesis (measured with either [5-3H]-, [3-14C]-, or [5-14C]mevalonate). However, [5-3H]mevalonate's rate of conversion into [3H]H2O (measure of shunted mevalonate carbon) was equivalent or greater than that measured for neutral isopentenoid lipid synthesis. [5-14C]Mevalonate radioactivity was incorporated into macromolecules and n-fatty acids. Kc cell extracts (100,000 X g supernatant fluid) readily oxidized alcohols with the following activity sequence: geraniol = nerol greater than farnesol = dimethylallyl alcohol greater than geranylgeraniol, isopentenyl alcohol, and allyl alcohol. Oxidation required NAD, and ethanol was not a substrate. We conclude that (a) Kc cells shunted a significant fraction (greater than or equal to 40%) of their post-IPP carbon to prenols for oxidative catabolism and (b) that shunted mevalonate carbon may play a significant role in the mevalonate-mediated regulation of Kc cell HMG-CoA reductase activity.
mesh_terms: D000438:Alcohols / Q000378:metabolism; D000818:Animals; D002250:Carbon Radioisotopes; D002460:Cell Line; D004330:Drosophila / Q000196:embryology / Q000201:enzymology*; D045782:Hemiterpenes; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D007700:Kinetics; D008798:Mevalonic Acid / Q000378:metabolism / Q000494:pharmacology*; D009243:NAD / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014316:Tritium
chemical_list: D000438:Alcohols; D002250:Carbon Radioisotopes; D045782:Hemiterpenes; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D009943:Organophosphorus Compounds; D009243:NAD; D014316:Tritium; C004809:isopentenyl pyrophosphate; D006903:Hydroxymethylglutaryl CoA Reductases; D008798:Mevalonic Acid