## 4 Specific Prenylquinones
### Ulbiquinone
#### 4.1.2 Ubiquinone in Parasitic Protozoa  
Ubiquinones are antioxidants that are involved in mitochondrial bioenergetics activities in protozoa that use oxidative phosphorylation [136; 135]. Ubiquinones are also biosynthesized by parasites that live under low oxygen tension and do not possess mitochondria or possess only a remnant [135]. As explained above, it is suspected that anaerobic protozoa such as _Giardia_ may have suffered an endosymbiosis event with a mitochondria ancestor [38]. Moreover, these parasites do not seem to possess the mitochondrial complex II (succinate dehydrogenase), complex III (ubiquinol-cytochrome C reductase) and complex IV (cytochrome c oxidase) [156], indicating the absence of conventional mitochondrial electronic transport as an energetic source. However, in 1994, UQ-9 was detected at 5 to 50 fold lower amounts in _E. histolytica_ and 15 to 350 fold lower amounts in _G. intestinalis_ than in aerobic organisms [135]. Small amounts of UQ-10 were also detected in _Trichomonas fetus_[135]. The eventual functions of these prenylquinones in the abovementioned parasites remain poorly understood. Ubiquinones clearly functions as a mitochondrial electron carrier in aerobic parasites such as trypanosomatids. Species of _Leishmania_ present different homologs of UQs, with lateral chains varying in length from 7 to 10 isoprenic units, with UQ-9 being the predominant homolog. Promastigote forms of _Leishmania amazonensis_ presented only the homolog UQ-9, whereas amastigote forms presented the UQs with 7, 8, and 9 isoprene units [135]. The differences in respiratory capacity among the forms should be the factor responsible for this divergence in the UQ profile: it is known that promastigotes present well-developed mitochondria in comparison to the degenerate mitochondria observed in the amastigote stage (vertebrate intracellular stage) [157]. _Leishmania donovani_ promastigotes have mostly UQ-9, but UQ-8 and UQ-10 are also detectable. In addition, promastigotes of _Leishmania major_ have UQ-9 and UQ-8 in a minor proportion [135]. Unlike the promastigotes of _L donovani_ and _L. major_, the promastigotes of _Leishmania pifanoi_ contained equivalent concentrations of UQ-9 and UQ-10, but UQs containing 7 and 8 isoprenic units in the lateral chain were also detected in _L. amazonensis_ promastigotes [135]. The total UQ concentrations in _L. donovani_ promastigotes and promastigote and amastigote forms of _L. amazonensis_ were substantially higher than those in some aerobically grown yeasts. Among trypansamatids, [PERSON] et al. in 2006 concluded that epimastigote forms of _T. cruzi_ synthesize mainly UQ-9, which stimulated further studies on the importance of the trypanosomal enzyme solanesyl-diphosphate synthase (TcSPPS) [137]. Furthermore, the UQ content of procyclic forms of _T. brucei_ was studied by [PERSON] et al. in 1979 and by [PERSON] et al. in 1991. In both cases, UQ-9 was shown to be synthetized by this parasite [72; 136]. The asexual stages of _P. falciparum_, _Plasmodium lophurane_ and _Plasmodium knowlesi_ have an active and essential pathway for UQ-7,8,9 homologs [146]. In other _Plasmodium_ species, during asexual stages, some UQ homologs were not detected. For example, UQ-9 was not detected in _Plasmodium lerghei_ and neither was UQ-7 in _Plasmodium cynomolgi_. Surprisingly, in _P. falciparum_, the biosynthetic pathways of different UQ homologs showed selectivity for radiolabeled isoprenic donors (IPP, FPP, GGPP) [138], which was suggested to be due to prenyltransferase/prenysynthase selectivity for different isoprenic moieties [138]. Similar to trypansamoids, the biological role of different UQ homologs in _Plasmodium_ is poorly understood, but some authors have suggested that these compounds are involved in different types of oxidative stress [138].