Carotenoids are synthesized from acetyl-CoA via the mevalonate pathway in fungi and plant cytosol/endoplasmic reticulum or from glyceraldehyde-3-phosphate and pyruvate via methylerythritol pathway in bacteria and plastids of plants. The first carotenoid phytoene is formed by successive condensations of isopentenyl pyrophosphate. Subsequently phytoene is conversed to various other carotenoids by dehydrogenation, cyclization, hydroxylation, epoxidation/de-epoxidation reactions. Enzymes involved in carotenoid ...