Studies on prenylquinones in green leaves

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Distributions and redox levels of prenylquinones in leaves and chloroplasts were studied using the methods developed here. The method is consisted of rapid extraction of the quinones on the sample preparation cartridge, followed by the separation and detection with the reversed-phase high-performance liquid chromatography using the dual-electrodes voltanmetric detector.1. More than half of plastoquinones in thylakoid membranes were found in lipid matrix, suggesting its role as mobile electron and proton carrier. The rest of plastoquinones were in particles as fixed electron/proton carriers. The molar ratios of each derivatives to chlorophyll were almost the same in every part of thylakoid membrane. Phylloquinone was concentrated in photosytem I particle, possibly as a redox component. The ratio of tocopherolquinone to chlorophyll was almost constant in every portion of thylakoid membrane, suggesting its role as a protectant for the photoinjury of pigment systems by strong light.2. During the development of spinach leaves the ratio of plastoquinone-C to chlorophyll was increased, and of ubiquinone-9 was decreased. The ratios of the other prenylquinones were not changed. It seems that the role of the respiratory system as ATP producing system is partly replaced by the photosynthetic system in the course of leaf development. Plasstoquinone C might be produced by photochemical epoxydation of plastoquinone A.3. The primary photochemical reaction in Photosystem II required two plastoquinone A molecules.4. The redox potential of plastoquinone A in chloroplasts was +20 mV at pH 7.8.