Zeaxanthin 7,8-dioxygenase

Function and significance

Zeaxanthin 7,8-dioxygenase is a chromoplastic enzyme that catalyzes the oxidative cleavage of zeaxanthin at the 7,8 and 7',8' double bonds. This reaction produces crocetin dialdehyde and 3-hydroxy-β-cyclocitral. Crocetin dialdehyde is a precursor to crocetin and its glycosylated forms, crocins, which are the main pigments in saffron. The other product, 3-hydroxy-β-cyclocitral, is a volatile compound that contributes to the aroma of saffron.

More recent research has suggested that another enzyme, carotenoid cleavage dioxygenase 2 (CCD2), is the primary enzyme responsible for crocetin biosynthesis in saffron, rather than the originally described zeaxanthin 7,8-dioxygenase (often referred to as ZCD or CsZCD). This has led to some debate in the scientific literature regarding the precise role and classification of zeaxanthin 7,8-dioxygenase.

The reaction catalyzed by this class of enzymes is of significant commercial interest due to the high value of saffron as a spice and natural food colorant.

References

References

1. (January 2003). "Oxidative remodeling of chromoplast carotenoids: identification of the carotenoid dioxygenase CsCCD and CsZCD genes involved in Crocus secondary metabolite biogenesis". The Plant Cell.
2. (August 2014). "Novel carotenoid cleavage dioxygenase catalyzes the first dedicated step in saffron crocin biosynthesis". Proc Natl Acad Sci U S A.