VITAMIN K, AN ESSENTIAL FACTOR FOR THE PHOTOCHEMICAL ACTIVITY OF ISOLATED CHLOROPLASTS

Abstract

As the result of the repetition of an experiment by French and Lynch on the function of carotene in photosynthesis, it was hypothesized that there were other petroleum ether-soluble substances with catalytic properties in the chloroplasts. Samples of freeze-dried chloroplasts were extracted with cold petroleum ether, and fractionated. Menadione (naphthoquinone, vitamin K) was found capable of restoring photochemical activity to extracted chloroplasts under conditions where the effect of purified [alpha]-and [beta]-carotene is negligible by comparison (partially purified B-carotene is as effective as vitamin K3). Similar results were obtained by vitamin K5. The experiments make it unlikely that the carotenoids function in the way various naphthoquinones do, but do indicate a new and rather specific role for vitamin K in photosynthesis.