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.