STAGE-SPECIFIC ISOFORMS OF COMPLEX-II (SUCCINATE-UBIQUINONE OXIDOREDUCTASE) IN MITOCHONDRIA FROM THE PARASITIC NEMATODE, ASCARIS-SUUM

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 hom 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 K-m 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 b(558)) of the adult enzyme did not cross-react with that of the larval enzyme. These results suggest that larval complex II differs hom 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.