Free-living nematodes Caenorhabditis elegans possess in their mitochondriaan additional rhodoquinone, an essential component of the eukaryotic fumarate reductase system

The respiratory chain of Caenorhabditis elegans was characterized in mitoch ondria isolated from aerobically grown nematodes. Nematode mitochondria con tain ubiquinone-9 as a major component and rhodoquinone-9 as a minor compon ent. The ratio of ubiquinone-9/rhodoquinone-9 is higher in C. elegans mitoc hondria than in mitochondria from second-stage larvae of Ascaris suum, the free-living stage of porcine gut-dwelling nematode. The individual oxidored uctase activities comprising succinate oxidase and the amount of substrate- reducible cytochromes are comparable to those of mitochondria from second-s tage larvae of A. suum, The specific activity of fumarate reductase is lowe r in C. elegans mitochondria than in mitochondria from second-stage larvae of A. suum, but still higher than in mammalian mitochondria. These results indicate that the free-living nematode C. elegans is capable of synthesizin g rhodoquinone, as distinguished from aerobic mammalian species, although i ts mitochondria appear more aerobic than A. suam larval mitochondria. (C) 1 999 Academic Press.