Mechanism of biopetrin-dependent enzymes

Phenylalanine hydroxylase has biopterin cofactor 1st reaction is a hydroxylation reaction by phenylalanine hydroxylase (PAH), a non-heme-iron containing homotetrameric enzyme. Requires O2, FeII, and biopterin. Pterins have a pteridine ring (similar to flavins)

Tetrahydrobiopterin Fe2+ also required for activity Only a few enzymes require tetrahydrobiopterin Important in biosynthesis of dopa, norepinephrine, epinephrine, and serotonin

Reaction Catalyzed by Phenylalanine Hydroxylase NIH shift [1,2] migration

Overall the reaction is considered a mixed function oxidation because one O atom of the O2 is reduced to water while the other is  incorporated into the amino acid product.

Phenylalanine Hydroxylase includes a non-heme iron atom at its active site. X-ray crystallographic analysis has shown that the following are ligands to the iron atom His nitrogen, Glu oxygen, and water oxygen atoms.

Mechanism of the Reaction Catalyzed by Tetrahydrobiopterin-dependent Monooxygenases nucleophilic substrate discussed with heme-dependent enzymes

What is NIH mechanism rearrangement where a hydrogen atom on an aromatic ring undergoes an intramolecular migration primarily during a hydroxylation reaction. This process is also known as a 1,2-hydride shift. These shifts are often studied and observed by isotopic labelling. An example of an NIH shift is shown below: An NIH shift is a chemical

Mechanism of NIH

In this example, a hydrogen atom has been isotopically labeled using deuterium (shown in red). As the hydroxylase adds a hydroxyl (the -OH group), the labeled site shifts one position around the aromatic ring relative to the stationary methyl group (-CH3).

Several hydroxylase enzymes are believed to incorporate an NIH shift in their mechanism, including tetrahydrobiopterin- dependent hydroxylases. The name NIH shift arises from the U.S. National Institutes of Health from where studies first reported observing this transformation.