Light-Dependent Conversions of Endogenous α-Tocopherylquinone and Plastoquinone-D in Spinacia Oleracea Chloroplasts

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Abstract
Measurement of the endogenous levels of [alpha]-tocopherylquinone, plastoquinone-D, and plastoquinone-(A+B) in fragmented spinach chloroplasts was carried out. Thin-layer chromatography was used to isolate the quinones. It was possible to measure oxidized quinone before and after a mild oxidation treatment and thus, by difference, obtain a measure of the hydroquinone concentration. Data are presented which indicate that these quinones apparently exist in a state of dynamic equilibrium which is sensitive to light and dark conditions. o-Phenanthroline at 10-4 [image] inhibits the light-induced changes in quinone levels. This further implicates these quinones as redox intermediates in electron transfer reactions associated with the photosynthetic process.