Metabolism of Carotenoids by Enzymes of Oxygen Metabolism

Summary

Carotenoids are metabolized by lipoxygenases and other oxygenases in bacteria, plants and animals; however, the mechanisms of these reactions are poorly understood. We have studied the oxidation of β-carotene by soybean lipoxygenase as a model system for understanding these reactions in vivo. β-carotene inhibits the rate of peroxidation of linoleic acid and the production of linoleic hydroperoxide product in a concentration-dependent fashion. In the presence of soybean lipoxygenase, carotenoid absorbance at 452 nm is rapidly diminished (bleached), however, we have not yet been able to identify the carotenoid metabolites. Although autoxidation products were identified, no enzyme-dependent carotenoid metabolite absorbing over the range of 300 to 600 nm was eluted from reverse phase HPLC columns. Experiments are in progress to identify the enzymatic metabolites. Hydroperoxide products of lipoxygenases are precursors to leukotrienes and other cytokines, the production of which are associated with a number of inflammatory and allergic states. As β-carotene is associated with enhancement of the immune response, the inhibition of lipoxygenase products in vivo may represent an important mechanism by which carotenoids serve in immunoregulation.