Biosynthesis Pathway for Vitamin A
geranylgeranyl diphosphate (GGDP)
GGDP occurs naturally in rice endosperm.
Two molecules of GGDP are used in this process.
phytoene synthase. A gene taken from daffodil is responsible for producing the enzyme phytoene synthase. The gene is controlled by a rice promoter and is only expressed in the endosperm (Toenniessen 2000). Phytoene synthase catalyzes the reaction that converts two GGDP molecules to phytoene, the first step in provitamin-A synthesis.
Phytoene desaturase, an enzyme originating from the bacterium Erwinia uredovora, catalyzes two steps in the pathway. A total of four double bonds are introduced to convert phytoene to lycopene (Ye et al. 2000; McLaren and Frigg 2001).
Lycopene b-cyclase, also originating
Once ingested, our body cleaves provitamin A at its central carbon-carbon bond resulting in vitamin A (retinol) (Carey 1987).
Vitamin A (retinol)
Jason Sutton in the Department of Bioagricultural
Sciences and Pest Management at Colorado State University contributed the
content for this page.
Jason Sutton in the Department of Bioagricultural Sciences and Pest Management at Colorado State University contributed the content for this page.