ISOLATION AND PARTIAL CHARACTERIZATION OF AN 18-KDA CAROTENOID-PROTEIN COMPLEX FROM CARROT ROOTS

A carotenoid-protein complex was isolated, purified, and partially cha racterized from carrot juice by detergent treatment followed by ammoni um sulfate precipitation, gel filtration, and ion exchange chromatogra phy. Results from SDS-urea-PAGE analysis indicated that the complex co ntained a major protein subunit with a molecular mass of 18 kDa. HPLC analysis of the pigments associated with this complex indicated that b eta-carotene, alpha-carotene, and lutein were the major carotenoids pr esent along with small amounts of phytoene and zeta-carotene. Carrot c hromoplast subfractionation and sucrose density centrifugation also re sulted in a major carrot pigment fraction which was enriched in the 18 kDa protein. The 18 kDa protein-containing-carotenoid complex is the major complex associated with noncytosolic carrot pigments within the carrot chromoplasts. The relative concentrations of both 18 kDa protei n and total carotenoids present in chromoplasts indicate that the caro tenoid-protein complex is only associated with a small percentage of t otal carrot carotenoids. It is thus unlikely that the 18 kDa protein i nfluences carotenoid bioavailability from carrots. This carotenoid-pro tein complex may function enzymatically in carotenoid synthesis.