Changes and Their Control Mechanisms of Mitochondrial Electron-Transport Components During Ascaris Life Cycle

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1. The primary structure of the flavin-bound tryptic peptide from the Fp subunit of Ascaris adult complex II was determined and found to be highly similar to those of the corresponding flavin-binding regions of bovine heart and bacterial Fp subunits.The Ascaris Fp subunit was shown to contain two regions exhibiting striking sequence similarity to the segments interacting with the AMP moiety of FAD in bacterial Fp subunits.2. To elucidate mechanisms of aerobic-anaerobic respiratory transition during development of Ascaris nematode, the larval respiratory chain and its complex II (succinate-ubiquinone oxidoreductase) have been characterized in the isolated mitochondria by spectrophotometry, immunoblotting using anti adlt complex II antibodies and determination of quinones.The results obtained showed that L_2 larvae were the most aerobic among stages studied and the larval complex II was different from the adults counterpart. Furthermore, evidence showing biosynthetic conversion of quinones during development was obtained.3. Oxidation-reduction midpoint potentials (Ems) were determined at pH 7.0 for cytochromes in the anaerobic respiratory chain of Ascaris mitochondria by redox titration techniques.Cytochrome b_<558>, which is associated with complex II that functions as fumarate reductase in the terminal step of the respiratory chain, was shown to have an Em of -34 mV in the isolated complex II and -54 mV in mitochondria. These values are much higher than the value reported for mammalian cytochrome b_<560> of complex II, showing a unique feature of Ascaris cytochrome b_<558>.