phox . This was in agreement with the finding that a single base substitution (C1024 to T) changed His-338 to Tyr in gp91 phox in a predicted FAD-binding domain of the flavocytochrome model. The loss of FAD could not be corrected even after addition of reagent FAD or a FADrich dehydrogenase fraction isolated from normal neutrophils to the patient's membranes, in a reconstitution in vitro with normal cytosol. These results indicate that His-338 is a very critical residue for FAD incorporation into the NADPH oxidase system. This is the first such mutation found in CGD.

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.

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The survival of parasites is dependent on that of the host. It is considered that parasites originated from nonparasitic ancestors and adapted to the environment in the host during the evolutional process, and developed hostand organ-specificities. Regarding energy metabolism, which is an essential factor for the survival, parasites adapt to the environment under a low oxygen tension in the host using metabolic systems which are very different from that of the host mammals. In such systems, parasite mitochondria play diverse roles. Especially, marked changes in the morphology and components of the mitochondria in the life cycle are very interesting in biological aspects such as developmental control and environmental adaptation. Such unique properties of parasite mitochondria could be promising targets for chemotherapy.