Maize embryos are endowed with the ascorbate biosynthetic system and the last enzyme of the pathway, galactono oxidase (or dehydrogenase), is very active; L-galactono-γ-lactone addition gives rise to a 3-fold increase in cellular ascorbate content. Lycorine, an alkaloid extracted from members of the Amaryllidaceae, strongly inhibits the in vivo conversion of L-galactono-γ-lactone to ascorbic acid. Data reported here seem to suggest that lycorine forms a relatively stable association with galactono oxidase; incubation with 50 μM lycorine shows a marked inhibitory effect that persists when the alkaloid is removed from the incubation medium. The inhibitory effect of lycorine is significantly higher in onion roots and pea embryos in comparison with maize embryos. This different sensitivity to the alkaloid can be explained by the inability of onion and pea to overcome the decrease in ascorbate biosynthesis by means of dehydroascorbate reductase, which has a significantly lower activity in these two species than that in maize embryos. Galactono oxidase also efficiently utilizes L-gulono-γ-lactone, the physiological substrate of the animal enzyme. Considering that lycorine induces scurvy-like symptoms in ascorbic acid-synthesizing animals, it is reasonable to suppose that lycorine inhibits ascorbate biosynthesis in both plants and animals by acting on the last step in the biosynthetic pathway leading from sugar to ascorbate.

"In vivo" inhibition of galactono-g-lactone conversion to ascorbate by lycorine

PACIOLLA, Costantino;TOMMASI, Franca;
1994

Abstract

Maize embryos are endowed with the ascorbate biosynthetic system and the last enzyme of the pathway, galactono oxidase (or dehydrogenase), is very active; L-galactono-γ-lactone addition gives rise to a 3-fold increase in cellular ascorbate content. Lycorine, an alkaloid extracted from members of the Amaryllidaceae, strongly inhibits the in vivo conversion of L-galactono-γ-lactone to ascorbic acid. Data reported here seem to suggest that lycorine forms a relatively stable association with galactono oxidase; incubation with 50 μM lycorine shows a marked inhibitory effect that persists when the alkaloid is removed from the incubation medium. The inhibitory effect of lycorine is significantly higher in onion roots and pea embryos in comparison with maize embryos. This different sensitivity to the alkaloid can be explained by the inability of onion and pea to overcome the decrease in ascorbate biosynthesis by means of dehydroascorbate reductase, which has a significantly lower activity in these two species than that in maize embryos. Galactono oxidase also efficiently utilizes L-gulono-γ-lactone, the physiological substrate of the animal enzyme. Considering that lycorine induces scurvy-like symptoms in ascorbic acid-synthesizing animals, it is reasonable to suppose that lycorine inhibits ascorbate biosynthesis in both plants and animals by acting on the last step in the biosynthetic pathway leading from sugar to ascorbate.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11586/133222
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