Biochemical studies on aerobic-anaerobic respiratory transition in mitochondria from parasitic helminthes

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1. The primary structures of the Ip subunit of complex II of adult Ascaris were determined using peptides separated on Biogel P-60 in the presence of sodium dodecylsulfate. The alanine-threonine cluster, a conserved region in the amino terminus of the mammalian Ip subunit, was found in the Ascaris Ip subunit. Two of the three cystein-rich segments generally conserved in the Ip subunit were sequenced following chemical modification of cystein residues. From a comparative analysis of the sequences, the Ip subunit of complex II in Ascaris adult appears to be more closely related to those of bacterial SDH and mammalian complex II than to that of bacterial FRD, even though Ascaris complex II shows a high FRD activity.2. To elucidate mechanisms of aerobic-anaerobic respiratory transition during development of Ascaris nematode, the larval respiratory chain and its complex II have been characterized in the isolated mitochondria by spectrophotometry, immunoblotting using anti adult complex II antibodies and determination of quinones. The results obtained showed that L2 larvae were the most aerobic among stages studied and the larval complex II was different from the adult counterpart. Furthermore, evidence showing biosynthetic conversion of quinones durig development was obtained.3. Mitochondria from a lung fluke, Paragonimus westermani, were isolated to study the worm respiratory chain. Interestingly, the adult worm mitochondria were shown to possess both aerobic and anaerobic respiratory chains, i. e., cyanide-sensitive succinate oxidase and NADH-fumarate reductase system, respectively. The mitochondria were also found to contain both rhodoquinone-10 and ubiquinone-10.