Ubiquinone-2 (1) was oxidized to 6-[7-carboxy-3-methyl- (2E, 6E)-2, 6-octadienyl]-2, 3-dimethoxy-5-methyl-1, 4-benzoquinone (2) and 6-[6, 7-dihydroxy-3, 7-dimethyl- (E)-2-octenyl]-2, 3-dimethoxy-5-methyl-1, 4-benzoquinone (3) by the 6000×g supernatant of guinea-pig liver homogenate in the presence of nicotinamide-adenine dinucleotide (NAD)- and dihydronicotinamideadenine dinucleotide phosphate (NADPH)-generating systems.