Stage-specific Isoforms of Complex II (Succinate-Ubiquinone Oxidoreductase) in Mitochondria from the Parasitic Nematode, Ascaris suum

Abstract

Complex II from mitochondria of the adult parasitic nematode, Ascaris suum, exhibits high fumarate reductase activity and plays a key role in the anaerobic electron transport observed in these organelles. In contrast, mitochondria isolated from free living second stage larvae (L2) of A. suum show much lower fumarate reductase activity than those from adults, whereas succinate dehydrogenase activities of mitochondria in both stages are comparable. In the present study, biochemical and antigenic properties of the partially purified enzymes from both larval and adult mitochondria were compared. Larval complex II eluted from the DEAE-Cellulofine column chromatography at a lower salt concentration than adult enzyme, whereas the apparent molecular size of both enzyme complexes estimated by gel permeation column chromatography was the same. The fumarate reductase activity of larval complex II was less than 3% of that of adult enzyme, and the Km values for substrates were significantly different between the two complexes. The flavoprotein subunit of larval complex II could be distinguished from that of adult complex II by two-dimensional gel electrophoresis and peptide mapping. The antibody against the smallest subunit (small subunit of cytochrome b558) of the adult enzyme did not cross-react with that of the larval enzyme. These results suggest that larval complex II differs from adult enzyme and is more similar to aerobic mammalian enzymes with low fumarate reductase activity. This is the first direct indication of the two different stage-specific forms of mitochondrial complex II.

Two Hydrophobic Subunits Are Essential for the Heme b Ligation and Functional Assembly of Complex II (Succinate-Ubiquinone Oxidoreductase) from Escherichia coli

“…A tighter association between the catalytic portion and cytochrome b in mitochondrial complex II compared with the bacterial enzyme may explain this difference. Active mitochondrial complex II is eluted from the gel filtration column in the presence of an anionic detergent, Sarkosyl (41,45), while cytochrome b 556 in E. coli complex II is dissociated from the complex and can be purified by the same column (35); this supports the above idea. A difference in the biogenesis of the enzyme complex was also found between complex II and FRD of E. coli.…”

“…The higher ratio of succinate-ubiquinone oxidoreductase to SDH in membranes from pSDHCDAB as compared with other membranes (Table III) may be related to the high content of cytochrome b 556 . The association of heme b in mitochondrial complex II is still unclear except for A. suum complex II (21,45), even though the genes for SDH3 and SDH4 from S. cerevisiae (14 -16) and the cDNA for bovine cybL (17,18) have been cloned and sequenced. Our present report is the first indication that both hydrophobic subunits are indispensable for heme b ligation into the two-subunit cytochrome b in complex II.…”

A structural moDAl for the membrane‐integral domain of succinate:quinone oxidoreductases

“…Anaerobic cells respiring with fumarate as terminal electron acceptor contain quinol:fumarate reductase (QFR) [6,7]. This enzyme is very similar to SQR in composition, and probably also in structure; in vitro QFRs and SQRs can generally both catalyse succinate oxidation and fumarate reduction, but at different rates.…”

Parasite Mitochondria as a Target for Chemotherapy.

“…21) Furthermore, while larvae complex II has only SQR activity as complex II in mammals, the enzyme in adult has high QFR activity, as well as SQR activity. On comparison of the peptide map and reactivity with antibodies against the subunits, at least Fp and Cyb S in complex II differed between larvae and adult.…”