The enzyme from Pseudomonas diminuta is specific towards N-containing N-heterocyclic substrates, including isoquinoline, isoquinolin-5-ol, phthalazine and quinazoline. Electron acceptors include 1,2-benzoquinone, cytochrome c, ferricyanide, iodonitrotetrazolium chloride, nitroblue tetrazolium, Meldola blue and phenazine methosulfate.