Major metabolic pathways and electron transport chain in mitochondria of the adult nematode Ascaris lumbricoides (giant roundworm). Major metabolic pathways and electron transport chain in mitochondria of the adult nematode Ascaris lumbricoides (giant roundworm). The map is redrawn based on data reported previously (249). Mature forms of this animal, a large and very common parasitic worm, inhabit the small intestine of their hosts. Like most parasitic worms, Ascaris performs malate dismutation to obtain redox balance and uses rhodoquinone to donate electrons for fumarate reduction (434). However, Ascaris is unusual, as acetyl-CoA and propionyl-CoA are used for the production of two branched-chain fatty acids, 2-methylbutanoate and 2-methylpentanoate, which are formed by the condensation of an acetyl-CoA and a propionyl-CoA or two propionyl-CoAs, respectively, with the subsequent reduction of the condensation products (436, 437). These short branched-chain fatty acids are typical end products for Ascaris (249, 251, 298). Abbreviations: MOP-CoA, 2-methyl-3-oxo-pentanoyl-CoA; MOB-CoA, 2-methyl-3-oxo-butanoyl-CoA; CI to CIV, respiratory complexes I to IV; UQ, ubiquinone; RQ, rhodoquinone; C, cytochrome c; A, ATPase; FRD, fumarate reductase; [2A, B], acetate:succinate CoA-transferase (subfamilies A and B); [3], succinyl-CoA synthetase; [5], malic enzyme; [6], pyruvate dehydrogenase complex; [8], fumarase; [11], malate dehydrogenase; [14], methylmalonyl-CoA mutase; [15], methylmalonyl-CoA epimerase; [16], propionyl-CoA carboxylase; [17], phosphoenolpyruvate carboxykinase (ITP/GTP dependent); [44], condensing enzyme; [45], 2-methyl acetoacyl-CoA reductase; [46], hydratase; [47], 2-methyl branched-chain enoyl-CoA reductase; [48], acyl-CoA transferase. The photograph shows Ascaris lumbricoides worms at the adult stage, with lengths of ca. 15 cm (top, male) and 30 cm (bottom, female). (Photograph by Rob Koelewijn, Harbor Hospital, Rotterdam, Netherlands.)‏ Miklós Müller et al. Microbiol. Mol. Biol. Rev. 2012; doi:10.1128/MMBR.05024-11