Enzymology of the carotenoid cleavage dioxygenases: reaction mechanisms, inhibition and biochemical roles.

Carotenoid cleavage dioxygenases (CCDs) are a large family of non-heme iron (II) dependent enzymes. CCDs catalyse the selective oxidative cleavage of carotenoids to produce apocarotenoids. Apocarotenoid derived molecules form important signalling molecules in plants in the form of abscisic acid and strigolactone and in mammals in the form of retinal. Very little is known biochemically about the CCDs and only a handful of CCDs have been biochemically characterised. Mechanistically, debate surrounds whether CCDs utilise a mono or dioxygenase mechanism. Here, we review the biochemical roles of CCDs, discuss the mechanisms by which CCD cleavage is proposed to occur, and discuss recent reports of selective CCD enzyme inhibitors.