Camalexin is a compound produced by Arabadopsis thaliana, used in plant defense. Its accumulation is induced by contact with parasites, and it inhibits the growth of those parasites. Synthesis of camalexin starts with L-tryptophan, which reacts using tryptophan N-monooxygenases 1 and 2 to form N-hydroxy-L-tryptophan. This then reacts using the same enzyme to form N,N-dihydroxy-L-tryptophan, which spontaneously forms (E)-indol-3-ylacetaldoxime. (E)-indol-3-ylacetaldoxime reversibly reacts with a indoleacetaldoxime dehydratase enzyme to form (Z)-indol-3-ylacetaldoxime, its isomer. The isomer then loses a water molecule via indoleacetaldoxime dehydratase again, forming 3-indoleacetonitrile. Another reaction with indoleacetaldoxime dehydratase forms 2-hydroxy-2-(1H-indol-3-yl0acetonitrile, which then reacts one final time with the indoleacetaldoxime dehydratase enzyme to lose a water molecule and form dehydro(indole-3-yl)acetonitrile. At this point, a glutatione molecule is added using glutatione S-transferase F6 to form (glutation-S-yl)(1H-indol-3-yl)acetonitrile. A water molecule is added by gamma-glutamyl peptidases 1 and 3, as well as glutathione hydrolase 3, forming L-glutamic acid as a side product, as well as (L-cysteinylglycin-S-yl)(1H-indol-3-yl)acetonitrile. An unknown enzyme then catalyzes a reaction that adds a water molecule and removes a glycine, forming 2-(cystein-S-yl)-2-(1H-indol-3-yl)-acetonitrile. Then, in a reaction using bifunctional dihydrocamalexate synthase/camalexin synthase, an oxygen molecule is added, a hydrogen ion, hydrogen cyanide molecule and water molecule are removed, and (R)-dihydrocamalexate is formed. Finally, the same enzyme catalyzes the formation of camalexin, the final product of this pathway.

Camalexin Biosynthesis References