Oxidation of 10-formyltetrahydrofolate to 10-formyldihydrofolate by complex IV of rat mitochondria.
We hypothesized that the unanticipated bioactivity of orally administered unnatural carbon-6 isomers, (6R)-5-formyltetrahydrofolate (5-HCO-THF) and (6S)-5,10-methenyltetrahydrofolate (5,10-CH-THF), in humans [Baggott, J. E., and Tamura, T. (1999) Biochim. Biophys. Acta 1472, 323-32] is explained by the rapid oxidation of (6S)-10-formyltetrahydrofolate (10-HCO-THF), which is produced by in vivo chemical processes from the above folates. An oxidation of 10-HCO-THF produces 10-formyldihydrofolate (10-HCO-DHF), which no longer has the asymmetric center at carbon-6 and is metabolized by aminoimidazole carboxamide ribotide (AICAR) transformylase forming bioactive dihydrofolate. Since cytochrome c (Fe(3+)) rapidly oxidizes both (6R)- and (6S)-10-HCO-THF [Baggott et al. (2001) Biochem. J. 354, 115-22], we investigated the metabolism of 10-HCO-THF by isolated rat liver mitochondria. We found that 10-HCO-THF supported the respiration of mitochondria without uncoupling ATP synthesis. The site of electron donation was identified as complex IV, which contains cytochrome c; the folate product was 10-HCO-DHF, and the reaction was saturable with respect to 10-HCO-THF. Both (6S)- (unnatural) and (6R)-10-HCO-THF supported the respiration of mitochondria, whereas (6S)-5-formyltetrahydrofolate (5-HCO-THF) was inactive. To our knowledge, this cytochrome c oxidation of 10-HCO-THF to 10-HCO-DHF in the mitochondrial intermembrane space represents a possible folate metabolic pathway previously unidentified and would explain the bioactivity of unnatural carbon-6 isomers, (6R)-5-HCO-THF and (6S)-5,10-CH-THF, in humans.
Brookes
Paul S
PS
Department of Pathology and Department of Nutrition Sciences, University of Alabama at Birmingham, 35294, USA.
Baggott
Joseph E
JE
D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004579:Electron Transport / Q000187:drug effects; D003576:Electron Transport Complex IV / Q000378:metabolism*; D005492:Folic Acid / Q000031:analogs & derivatives* / Q000378:metabolism*; D006207:Half-Life; D006868:Hydrolysis; D002955:Leucovorin / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D016877:Oxidants / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects; D011190:Potassium Cyanide / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D016877:Oxidants; C010161:10-formyltetrahydropteroylglutamic acid; C055914:10-formyldihydrofolate; D000968:Antimycin A; D005492:Folic Acid; D003576:Electron Transport Complex IV; D011190:Potassium Cyanide; D002955:Leucovorin