An intermediate of ubiquinone biosynthesis exists in the microsomal fraction of HepG2 cells.
We analyzed lipids extracted from human hepatoma HepG2 cells using a high performance liquid chromatograph equipped with a reversed phase column and found a compound with a mass spectrum showing certain diagnostic ion fragments of 1-methoxy-5-polyprenyl-phenol, a known intermediate of ubiquinone biosynthesis. Universally radiolabeled [14C]-p-hydroxybenzoate, a precursor of ubiquinone, was incorporated into the compound on incubation with the cells, suggesting that the compound is a precursor of ubiquinone. The presence of the compound in the microsomal fraction of HepG2 cells was not due to contamination by the mitochondrial fraction because the activity of succinate-cytochrome c reductase in the microsomal fraction was below 1% of that in the mitochondrial fraction, whereas the contents of ubiquinone and the compound in the former were 4.6 and 7.8% of those in the latter, respectively. These results support the hypothesis that ubiquinone biosynthesis might occur in microsomes as well as mitochondria.
Kang
D C
DC
Department of Biochemistry, Kyushu University School of Medicine, Fukuoka.
Takeshige
K
K
Minakami
S
S
D002851:Chromatography, High Pressure Liquid; D006801:Humans; D008862:Microsomes, Liver / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000201:enzymology; D013384:Succinate Cytochrome c Oxidoreductase / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014451:Ubiquinone / Q000096:biosynthesis*
D014451:Ubiquinone; D013384:Succinate Cytochrome c Oxidoreductase