Subsystem: Isoprenoid Biosynthesis: Interconversions
This subsystem's description is:
Major terpenoid building blocks, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), are produced via two different biosynthetic routes: in some species by the so-called mevalonate pathway, and in others by the non-mevalonate or DOXP pathway. Both pathways produce the same key building blocks (IPP and DMAPP), essential in all forms of cellular life. They have apparently involved completely independently, and they share only one enzyme – Isopentenyl-diphosphate delta-isomerase (IPDDI). Historically the mevalonate pathway and its enzymes were thoroughly studied in eukaryotes. Some bacteria also use mevalonate pathway, and all of the corresponding genes were identified based on homology with eukaryotic counterparts [Ref.2,3]. Although usually bacteria have only one of the two pathways, there are exceptions: Listeria has boths. Plants also have both, but one of them (DOXP) is of plastid (bacterial) origin. All other eukaryotes and archaea appear to have only mevalonate pathway. ISPC seems to be a missing gene in Brucella ssp. Reconstruction of the mevalonate pathway in archaea including conjectures for some locally missing genes was described [Ref.4]. The alternative DOXP pathway, characteristic of most bacteria was not recognized until very recently (for a review see [Ref.5]), and some aspects of it remained obscure until recently [Ref.6,7].
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