A shared mechanistic pathway for pyridoxal phosphate–dependent arginine oxidases

Significance

Pyridoxal phosphate (PLP)-dependent enzymes rarely react with oxygen, but an emerging group of oxygen-, PLP-dependent enzymes oxidize
l
-arginine. Two types of oxidases are known: hydroxylases and desaturases. We demonstrate that arginine desaturases have a minor hydroxylase activity and then show through X-ray crystallographic, mutagenesis, spectroscopic, and computational studies that their mechanism involves two rounds of single-electron transfer to oxygen and superoxide rebound, ultimately giving a conjugated hydroperoxyl intermediate. Water can attack to give a hydroxylated product and release H
2
O
2
, but with water absent, the intermediate can be deprotonated, instead giving a desaturated product and H
2
O
2
. Our work outlines the unique mechanism and evolutionary history of these enzymes and sets the stage toward engineering these enzymes to catalyze oxidative reactions.