Nature, intracellular distribution and formation of terpenoid quinones in Euglena gracilis

Abstract

1. Light-grown cells of Euglena gracilis strain Z, var. bacillaris and 1224/5g contain phylloquinone, plastoquinone, alpha-tocopherol, alpha-tocopherolquinone and ubiquinone-9 (i.e. ubiquinone with 9 isoprene units/mol.). 2. The concentration (per g. dry wt.) of plastoquinone (and chlorophyll) in light-grown cells of strain Z was governed by the composition of the culture medium and age of the cells. Highest yields of plastoquinone were obtained under autotrophic conditions, the concentration reaching a maximum after 6-8 days' growth. The concentrations were less in heterotrophic media. The concentration of ubiquinone was relatively unaffected by the age of the cells or composition of the medium. 3. In light-grown cells of strain Z plastoquinone, alpha-tocopherolquinone and alpha-tocopherol were mainly localized in the chloroplast; ubiquinone was found to be in the mitochondria. 4. Etiolated (dark-grown) cells of strain Z contained no phylloquinone, plastoquinone or alpha-tocopherolquinone; alpha-tocopherol was present in lower concentrations compared with light-grown cells; ubiquinone concentrations were similar to those for light-grown cells. The presence of alpha-tocopherol in etiolated cells suggested that this chromanol was not entirely confined to the chloroplast. 5. On illumination of etiolated cells of strain Z the chloroplastidic components plastoquinone, alpha-tocopherolquinone and alpha-tocopherol were synthesized in step with chloroplast formation. Ubiquinone concentrations, as expected, were unaffected. 6. [2-(14)C]Mevalonic acid, the specific distal terpenoid precursor, was not incorporated into any of the terpenoid components examined. This was attributed to the impermeability of the cell wall to this compound, rather than to a novel pathway of terpenoid biosynthesis.