Triple hydroxylation of tetracenomycin A2 to tetracenomycin C involving two molecules of O(2) and one molecule of H(2)O.

The TcmG or ElmG oxygenase-catalyzed triple hydroxylation of tetracenomycin (Tcm) A2 to Tcm C proceeds via a novel monooxygenase-dioxygenase mechanism, deriving the 4- and 12a-OH groups of Tcm C from two molecules of O(2) and the 4a-OH group of Tcm C from a molecule of H(2)O. These results suggest a mechanistic analogy among TcmG, ElmG, and the bacterial and fungal hydroquinone epoxidizing dioxygenases, as well as the mammalian vitamin K-dependent gamma-glutamyl carboxylase.