ISOLATION AND PARTIAL CHARACTERIZATION OF ALPHA-CAROTENE-CONTAINING AND BETA-CAROTENE-CONTAINING CAROTENOPROTEIN FROM CARROT (DAUCUS-CAROTA L) ROOT CHROMOPLASTS

A simple procedure for the isolation and purification of carotenoproteins from carrot root (Daucus carota L.) chromoplasts was developed. The procedure involved isolation and lysis of the chromoplasts and gel filtration to yield one major protein complexed with alpha- and beta-carotene. The native carotenoprotein complex has a molecular weight of over 2 million. Isoelectric focusing analysis indicated a single prominent protein with a pI of 3.8 and minor protein with pI of 3.6. SDS-PAGE analysis showed single protein subunits of MW 54 000. These data, along with other research papers, suggest the native protein consists of long polymeric chains of MW 54 000 protein subunits. HPLC analysis demonstrated that one molecule of alpha-carotene and two molecules of beta-carotene were bound to each 54-kDa subunit. The same molar ratio of alpha- to beta-carotene exists in the carrot. This work shows the existence of a specific alpha- and beta-carotene binding protein complex in carrots.