Ubiquinone metabolism

Ubiquinone, also known as coenzyme Q is an integral component of electron transport chain. In electron transport chain of inner mitochondrial membrane, ubiquinone acts as an electron carrier transferring electrons from NADH dehydrogenase (complex I), malate:quinone oxidoreductase and succinate dehydrogenase (complex II) to cytochrome bc1 complex (complex III). In the case of Cryptosporidia, the electrons are transferred to the alternative oxidase (electron transport chain). Ubiquinone is synthesised from chorimsate, which is salvaged from host as shikimate pathway is absent. The other important co-substrates involved in this pathway are glutamine, isoprenoids (terpenoid metabolism) and S-adenosyl methionine (methionine metabolism). This pathway is identical in Toxoplasma, Plasmodia, Cryptosporidia and Piroplasma species and two enzymes, oxo-acid lyase and 3-octaprenyl-4-hydroxybenzoate carboxy-lyase are missing in the genomes of all apicomplexan species.


Enzyme EC Number Gene id
UbiB Hydroxylase


FAD-dependent monooxygenase 1.14.13.- Chro.80315
Ubiquinone/menaquinone biosynthesis methyltransferase 2.1.1.- Chro.10320
3-demethylubiquinone-9 3-O-methyltransferase Chro.20298
3-demethylubiquinone-9 3-O-methyltransferase Chro.50409
p-hydroxybenzoate-polyprenyltransferase 2.5.1.- Chro.30285
3-octaprenyl-4-hydroxybenzoate carboxy-lyase 4.1.1.- Missing in annotation
Oxo-acid  lyase 4.3.1.- Missing in annotation
Coq4 none Chro.10049
ABC1 protein required for ubiquinone biosynthesis none Chro.80377


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Sources and fates of metabolites


Substrate Source pathways Product Fate pathways
Chorismate Host Pyruvate Pyruvate metabolism
Glutamine Glutamate metabolism Glutamate Glutamate metabolism
All-trans-Geranyl-Geranyl-PP Terpenoid metabolism    
S-adenosylmethionine Methionine metabolism S-adenosylhomocysteine Methionine metabolism