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Carotenoids are a type of terpenoid that can be produced in the laboratory by mimicking natural processes. They are yellow to red dyes found in fruits and vegetables and serve as antioxidants and sometimes possess vitamin A activity. Carotenoids are synthesized in nature through two pathways, mevalonate and non-mevalonate. The gene coding for enzymes in carotenoid biosynthesis has been identified, making industrial production practical. The carotenoid pathway in plants may be manipulable via gene transfer technology, allowing for simpler and cheaper biosynthesis methodologies.
Terpenoids, also called isoprenoids, are organic compounds whose carbon skeleton is derived from the connection of isoprene units (CH2=C(CH3)CH=CH2). Carotenoids, a subtype of terpenoids, are classified as 30-C, 40-C, and so on, based on their number of skeletal carbon atoms. They can be produced in the laboratory by biosynthesis, sometimes called biogenesis, by mimicking processes found in nature. Starting from small and simple molecules, such as isopentenyl diphosphate, the additions take place gradually in the presence of catalytic enzymes, until the final products are reached. Although the reactions are known for their chemical pathway, their production may involve the use of microbes.
Carotenoids, including β-carotene, lycopene and xanthophylls, are yellow to red dyes found in carrots, apricots, spinach and other fruits and vegetables. They serve two well-known essential purposes. Because they absorb light at the blue end of the spectrum, carotenoids extend the frequency range at which plants can engage in photosynthesis; they also protect the green pigment from oxidative photolytic damage. In addition to their antioxidant properties, some carotenoids possess vitamin A activity. Foods rich in carotenoids tend to be low in fat.
The synthesis of carotenoids in nature is accomplished by one of two known processes: one is mevalonate, the other is the non-mevalonate carotenoid biosynthesis pathway. Both pathways are similar once you reach isopentenyl pyrophosphate (IPP). The next step is conversion to dimethylallyl pyrophosphate (DMPP), then geranyl pyrophosphate (GPP), and finally the 15-carbon species, farnesyl pyrophosphate (FPP). This serves as an intermediate in further steps of carotenoid biosynthesis. Two of the 15-carbon structures can be joined to form 30-C carotenoids using a catalyst.
If the intent is rather to produce 40-C or 50-C carotenoids, farnesyl diphosphate receives another IPP to form the 20-carbon intermediate, geranylgeranyl diphosphate (GGPP). This is then enzymatically added to itself to produce 40-C phytoene, which can be rearranged to lycopene. Once lycopene is reached, there are a variety of synthetic routes to different end results. Lycopene can be added further to produce 50-C carotenoids. Alternatively, the structures can be held at 40 carbon atoms and be catalytically converted into α-carotene or β-carotene, which initiate the third and fourth pathways.
Knowledge of the pathways of carotenoid biosynthesis has existed for decades. However, it was not until the 1990s that the gene coding for enzymes was sufficiently identified to make industrial production practical using methods found in nature. Gene cloning was performed for each of the phases of carotenoid biosynthesis, up to the production of xanthophylls. Molecular biologists believe that the carotenoid pathway in plants may be manipulable via gene transfer technology. This would allow for simpler and cheaper carotenoid biosynthesis methodologies.
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