The Reaction Specificity of Carotene Dioxygenase

The Reaction Specificity of Carotene Dioxygenase Whereasthe principal site of carotene dioxygenase attack is the 15,15 -central bond of p-carotene, there is evidence that asymmetric cleavage also occurs, leading to formation of 8 -, 10 -, and 12 -apo-carotenals, as shown in Figure 2.4. These apo-carotenals are metabolized by oxidation to apo-carotenoic acids, which are substrates for /3-oxidation to retinoic acid and a number of other metabolites. 

Redmond, T.M. et al.. Identification, expression, and substrate specificity of a mammalian beta-carotene 15,15-dioxygenase, J. Biol. Chem., 276, 6560, 2001. Leuenberger, M.G., Engeloch-Jarret, C., and Woggon, W.D., The reaction mechanism of the enzyme-catalyzed central cleavage of beta-carotene to retinal, Ang. Chem. Int. Ed., 40, 2614, 2001. 

Bacterial p-carotene hydroxylases, CrtZ, were characterized with respect to substrate specificity and reaction mechanism after expression in E. coli. The reactions depend on oxygen and are stimulated by 2-oxoglutarate, ascorbate, and Fe L which is typical for a dioxygenase reaction. Similar mechanistic properties were also found for bacterial ketolases encoded by crtW. These enzymes catalyze the introduction of... 

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