LYCORINE - A POWERFUL INHIBITOR OF L-GALACTONO-GAMMA-LACTONE DEHYDROGENASE-ACTIVITY

In vivo conversion of L-galactono-gamma-lactone to ascorbate is carrie d out in all of the plants that we have analysed. The enzyme catalysin g this reaction, i.e. L-galactono-gamma-lactone dehydrogenase, which a ppears to be localised in the mitochondrial membrane, is strongly inhi bited by lycorine: 5 mu M lycorine almost completely inhibits the acti vity of the enzyme. The alkaloid does not affect the activity of the a scorbate free radical reductase, dehydroascorbate reductase or ascorba te peroxidase. The results presented here confirm that lycorine is a s pecific inhibitor of ascorbate biosynthesis in plants, and, consequent ly, that it can be a useful tool to better understand the ascorbate me tabolism in ascorbate synthesising organisms.