4-hydroxybenzoate 3-monooxygenase (NAD(P)H)
4-Hydroxybenzoate 3-monooxygenase (NAD(P)H), also known as p-hydroxybenzoate hydroxylase, is an enzyme that catalyzes the chemical reaction:
4-hydroxybenzoate + NAD(P)H + H+ + O2 ⇌ 3,4-dihydroxybenzoate + NAD(P)+ + H2O
This enzyme belongs to the family of monooxygenases, specifically those that hydroxylate aromatic rings using NAD(P)H as a reductant. It plays a crucial role in the bacterial degradation of p-hydroxybenzoate, a common aromatic compound found in the environment.
The systematic name of this enzyme is 4-hydroxybenzoate,NAD(P)H:oxygen oxidoreductase (3-hydroxylating).
The enzyme requires NAD(P)H as a cofactor to function. It is a flavoprotein, meaning it contains a flavin prosthetic group, typically flavin adenine dinucleotide (FAD). The FAD acts as an electron carrier in the reaction.
The catalytic mechanism involves the binding of 4-hydroxybenzoate to the enzyme, followed by the reduction of FAD by NAD(P)H. Molecular oxygen then binds to the reduced flavin, forming a flavin hydroperoxide intermediate. This intermediate then hydroxylates the aromatic ring of 4-hydroxybenzoate at the 3-position, resulting in the formation of 3,4-dihydroxybenzoate (protocatechuate), NAD(P)+, and water.
4-Hydroxybenzoate 3-monooxygenase is found in various microorganisms, particularly bacteria such as Pseudomonas species. Its activity is important for the bioremediation of aromatic pollutants and for the carbon cycle in the environment. The protocatechuate produced by this enzyme is further metabolized through pathways such as the beta-ketoadipate pathway.
The enzyme has been extensively studied for its catalytic mechanism and structural properties. Its three-dimensional structure has been determined by X-ray crystallography, providing insights into its substrate binding site and catalytic center.