Figure 4: Monooxygenases involved in denitrification. (a) Conversion of 4-nitrophenol to p-benzaquinone by 4-nitrophenol 4-monooxygenase; (b) conversion of 4-nitrophenol to 4-nitrocatechol by 4-nitrophenol 2-monooxygenase; and (c) conversion of 2-nitrophenol to catechol by 2-nitrophenol 2-monooxygenase.