Biosynthesis of violacein: a genuine intermediate, protoviolaceinic acid, produced by VioABDE, and insight into VioC function

A biosynthetic intermediate of violacein produced by the mixed enzymes of VioABDE was elucidated to be 5-( 5- hydroxy1H- indol- 3- yl)- 3-( 1H- indol- 3- yl)- 1H- pyrrole- 2- carboxylic acid, named protoviolaceinic acid, indicating that VioC, responsible for the final biosynthetic step, works to oxygenate at the 2- position of the right side indole ring, and that the oxygenation reaction to form the central pyrrolidone core proceeds in a nonenzymatic fashion.