The Conversion of Lycopene-15,15'-3H to Cyclic Carotenes by Soluble Extracts of Higher Plant Plastids

Proof of the conversion of lycopene-15,15'- 3 H to neo-β-, α-, β-, δ-, and γ-carotenes by spinach chloroplasts and to neo-β- and β-carotenes by a soluble preparation of these plastids is presented in this paper. The conversion of lycopene-15,15'- 3 H to β-carotene by spinach chloroplasts was maximal when incubations were performed under nitrogen in light at 25° in the presence of NADP. When soluble preparations of spinach chloroplasts were used, an absolute requirement for FAD and a partial requirement for NADP were observed. Proof of the conversion of lycopene-15,15'- 3 H to cyclic carotenes by plastids, and by soluble extracts of plastids of fruit of "hi-β" and "hi-δ" tomato selections is also presented. Tritiated lycopene was converted to neo-β-, α-, β-, δ-, and γ-carotenes by hi-β tomato fruit plastids and to α-, β-, δ-, and γ-carotenes by a soluble preparation of these plastids. Both plastids and a soluble preparation of plastids of hi-δ tomato fruits converted tritiated lycopene to α-, β-, and δ-carotenes. Proof of the formation of the above cyclic carotenes from tritiated lycopene was obtained by chromatography with authentic carotenes on two different adsorbents. A close correspondence between radioactivity and optical density was observed for each carotene. Additional proof was obtained by crystallization of β-carotene to constant specific radioactivity and by gas-liquid chromatography of each hydrogenated carotene. Coincidence between mass and radioactivity of the hydrogenated carotenes was obtained. A mechanism is proposed for the formation of cyclic carotenes from lycopene.