Detection of ubiquinone in parasitic and free-living protozoa, including species devoid of mitochondria

Abstract

Ubiquinone (coenzyme Q, CoQ) was analyzed and individual homologues quantified in 11 species of parasitic and freeliving protozoa by a combination of thin-layer chromatography and high performance liquid chromatography. Fast atom bombardment ionization-mass spectrometry was used for the first time to confirm the identity of the fractionated CoQ homologues and proved to be a fast, gentle and convenient method for ubiquinone identification. Ubiquinone was detected in all organisms including those devoid of identifiable mitochondria. However, significantly lower levels of CoQ were present in those organisms lacking this respiratory organelle (5- to 50-fold lower in Entamoeba histolytica (CoQ 9) and 15- to 350-fold for Giardia lamblia (CoQ 9) and Tritrichomonas foetus (CoQ 10). Coenzyme Q 9 was the predominant homologue in promastigotes of Leishmania donovani and Leishmania major. Lower amounts of CoQ 8 and CoQ 10 were also detected in L. donovani and CoQ 8 in L. major. Comparison of the in vitro cultivated promastigote and amastigote forms of Leishmania pifanoi and Leishmania amazonensis revealed CoQ 9 to be the sole detectable ubiquinone homologue in the amastigote (macrophage) stage, whereas CoQ 8 and CoQ 10 were also present in the promastigotes (life cycle stage found in the insect gut) of L. pifanoi, and CoQ 7 and CoQ 8 in promastigotes of L. amazonensis. Interestingly, the total amounts of CoQ were similar in both forms of these organisms. The free-living ciliates, Tetrahymena thermophia and Paramecium tetraurelia contained CoQ 8 as the predominant ubiquinone species and this homologue was also present in the isolated cilia from P. tetraurelia. The marine ciliate, Parauronema acutum contained CoQ 7 as well as CoQ 8. Comparison of xenosome-containing P. acutum with organisms lacking the symbiont revealed that twice the level of CoQ 8 was present in cells grown with this cytoplasmic gram-negative bacterium. Results suggest that CoQ is ubiquitous amongst the protozoa, regardless of the presence of mitochondria, and may function in alternative roles to that of mitochondrial electron transport chain component.