Wax ester fermentation in mitochondria of the facultatively anaerobic photosynthetic flagellate Euglena gracilis. Wax ester fermentation in mitochondria of the facultatively anaerobic photosynthetic flagellate Euglena gracilis. The map is redrawn based on data reported previously (514). Under anaerobic conditions, this photosynthetic euglenid, which acquired its plastids through secondary endosymbiosis, uses acetyl-CoA produced by pyruvate:NADP+ oxidoreductase (419) as the terminal electron acceptor, leading to the formation of an unusual end product among eukaryotes: wax esters (213, 443, 514). Mitochondrial wax ester fermentation includes anaerobic fumarate respiration and the same propionyl-CoA formation pathway as the one found in mitochondria of facultative anaerobic animals excreting and/or accumulating propionate. Abbreviations: CI to CIV, respiratory complexes I to IV; UQ, ubiquinone; RQ, rhodoquinone; C, cytochrome c; A, ATPase; FRD, fumarate reductase; [3], succinyl-CoA synthetase; [5], malic enzyme; [6], pyruvate dehydrogenase complex; [7], pyruvate:NADP+ oxidoreductase; [8], fumarase; [9], pyruvate kinase; [10], phosphoenolpyruvate carboxykinase (ATP dependent); [11], malate dehydrogenase; [14], methylmalonyl-CoA mutase; [15], methylmalonyl-CoA epimerase/racemase; [16], propionyl-CoA carboxylase; [35], α-ketoacyl synthase; [36], β-ketoacyl reductase; [37], β-hydroxyacyl dehydrogenase; [38], trans-2-enoyl-CoA reductase. (Photograph of Euglena gracilis [American Type Culture Collection] by D. J. Patterson, L. Amaral-Zettler, M. Peglar, and T. Nerad, reprinted from the Encyclopedia of Life [http://eol.org/pages/918864/overview], which was published under a Creative Commons license.)‏ Miklós Müller et al. Microbiol. Mol. Biol. Rev. 2012; doi:10.1128/MMBR.05024-11