In vivo conversion of L-galactono-gamma-lactone to ascorbate is carried out in all of the plants that we have analysed. The enzyme catalysing this reaction, i.e. L-galactono-gamma-lactone dehydrogenase, which appears to be localised in the mitochondrial membrane, is strongly inhibited by lycorine: 5 mu M lycorine almost completely inhibits the activity of the enzyme. The alkaloid does not affect the activity of the ascorbate free radical reductase, dehydroascorbate reductase or ascorbate peroxidase. The results presented here confirm that lycorine is a specific inhibitor of ascorbate biosynthesis in plants, and, consequently, that it can be a useful tool to better understand the ascorbate metabolism in ascorbate synthesising organisms
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