Poster abstracts

Poster number 52 submitted by Carlo dela Sena

Substrate specificity of purified recombinant chicken β–carotene-9′,10′-oxygenase (BCO2)

Carlo dela Sena (Ohio State Biochemistry Program, The Ohio State University), Yan Yuan (Department of Human Nutrition, The Ohio State University), Sureshbabu Narayanasamy (Department of Human Nutrition, The Ohio State University), Kenneth M. Riedl, Steven J. Schwartz (Department of Food Science and Technology, The Ohio State University), Robert W. Curley, Jr. (Ohio State Biochemistry Program, College of Pharmacy, The Ohio State University), Earl H. Harrison (Ohio State Biochemistry Program, Department of Human Nutrition, The Ohio State University)

Abstract:
Dietary carotenoids such as β–carotene are oxidatively cleaved by β–carotene-15,15′-oxygenase (BCO1) at the central 15-15′ double bond to produce vitamin A. It has been shown that it cleaves hydroxylated carotenoids to a lower extent than β–carotene. Another carotenoid oxygenase, β–carotene-9′,10′-oxygenase (BCO2), cleaves carotenoids at the 9′-10′ double bond to produce an apo-10′-carotenoid and an ionone. In this work, we looked at the cleavage activity of BCO2 against major dietary carotenoids as well as apo-carotenals. Recombinant hexahistidine-tagged chicken BCO2 was expressed in Escherichia coli and purified by cobalt ion affinity chromatography. The purified protein was incubated with micellar solutions of test substrates at 20 μM, and the reaction mixtures were analyzed by high-performance liquid chromatography. Time-zero, no-enzyme and boiled-enzyme reactions were used as controls.
BCO2 cleaves hydroxylated carotenoids (zeaxanthin, lutein, β-cryptoxanthin) to a greater extent than their hydrocarbon counterparts such as β-carotene and α-carotene. Also, zeaxanthin and lutein, which both have a hydroxyl group in each of the two rings flanking the molecule, are cleaved to a greater extent than β-cryptoxanthin, which only has one hydroxylated ring. No cleavage activity was observed with lycopene, β–apo-8′-carotenal, β–apo-10′-carotenal, β–apo-12′-carotenal and β–apo-14′-carotenal under the conditions tested. In contrast, BCO1 has been shown to cleave the aforementioned apo-carotenals and lycopene, and has no activity with zeaxanthin and lutein.

Keywords: Carotenoids, vitamin A, BCO2