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 i n the anaerobic electron transport observed in these organelles. In co ntrast, mitochondria isolated from free living second stage larvae (L2 ) of A. suum show much lower fumarate reductase activity than those fr om 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 larva l and adult mitochondria were compared. Larval complex II eluted hom t he DEAE-Cellulofine column chromatography at a lower salt concentratio n than adult enzyme, whereas the apparent molecular size of both enzym e complexes estimated by gel permeation column chromatography was the same, The fumarate reductase activity of larval complex II was less th an 3% of that of adult enzyme, and the K-m values for substrates were significantly different between the two complexes. The flavoprotein su bunit of larval complex II could be distinguished from that of adult c omplex 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 larv al enzyme. These results suggest that larval complex II differs hom ad ult enzyme and is more similar to aerobic mammalian enzymes with low f umarate reductase activity, This is the first direct indication of the two different stage-specific forms of mitochondrial complex II.