rhodoquinone and fumaric-acid

Although schistosomes were thought to be one of the few parasitic helminths that do not produce succinate via fumarate reduction, it was recently demonstrated that sporocysts of Schistosoma mansoni produce, under certain conditions, succinate in addition to lactate. This succinate production was only observed when the respiratory chain activity of the sporocysts was inhibited, which suggested that succinate is produced by fumarate reduction. In this report the presence of essential components for fumarate reduction was investigated in various stages of S. mansoni and it was shown that, in contrast to adults, sporocysts contained a substantial amount of rhodoquinone which is essential for efficient fumarate reduction in eukaryotes. This rhodoquinone was not made by modification of ubiquinone obtained from the host, but was synthesized de novo. Furthermore, it was shown that complex II of the electron-transport chain in schistosomes has the kinetic properties of a dedicated fumarate reductase instead of those of a succinate dehydrogenase. The presence of such an enzyme, together with the substantial amounts of rhodoquinone, shows that in S. mansoni sporocysts succinate is produced via fumarate reduction. Therefore, the energy metabolism of schistosomes does not differ in principle from most other parasitic helminths, which are known to rely heavily on fumarate reduction.

Topics: Animals; Fumarates; Oxidation-Reduction; Schistosoma mansoni; Succinate Dehydrogenase; Succinic Acid; Ubiquinone

The Ascaris larval respiratory chain, particularly complex II (succinate-ubiquinone oxidoreductase), was characterized in isolated mitochondria. Low-temperature difference spectra showed the presence of substrate-reducible cytochromes aa3 of complex IV, c+c1 and b of complex III (ubiquinol-cytochrome c oxidoreductase) in mitochondria from second-stage larvae (L2 mitochondria). Quinone analysis by high-performance liquid chromatography showed that, unlike adult mitochondria, which contain only rhodoquinone-9, L2 mitochondria contain ubiquinone-9 as a major component. Complex II in L2 mitochondria was kinetically different from that in adult mitochondria. The individual oxidoreductase activities comprising succinate oxidase, and fumarate reductase were determined in mitochondria from L2 larvae, from larvae cultured to later stages, and from adult nematodes. The L2 mitochondria exhibited the highest specific activity of cytochrome c oxidase, indicating that L2 larvae have the most aerobic respiratory chain among the stages studied. The Cybs subunit of complex II in L2 and cultured-larvae mitochondria exhibited different reactivities against anti-adult Cybs antibodies. Taken together, these results indicate that the complex II of larvae is different from its adult counterpart. In parallel with this change in mitochondrial biogenesis, biosynthetic conversion of quinones occurs during development in Ascaris nematodes.

Topics: Animals; Ascaris suum; Cattle; Electron Transport Complex II; Fumarates; Larva; Mitochondria; Models, Biological; Multienzyme Complexes; Myocardium; NAD(P)H Dehydrogenase (Quinone); Oxidoreductases; Quinones; Succinate Dehydrogenase; Succinates; Succinic Acid; Ubiquinone