Enzyme - L-amino-acid oxidase

Alternative Name(s)
  • Ophio-amino-acid oxidase.

Catalytic Activity

L-alpha-amino acid + H2O + O2 = a 2-oxocarboxylate + H2O2 + NH4(+)



Reaction Mechanism

    L-aminoacid oxidase is a dimeric flavoprotein. it uses a non-covalently bound FAD cofactor in catalysing the stereospecific oxidative deamination of an L-amino acid substrate to an alpha ketoacid, forming ammonia and hydrogen peroxide. The enzyme shows a marked preference for hydrophobic amino acids including phenylalanine, tryptophan, tyrosine and leucine.

    The non-covalently bound FAD is first reduced to FADH2 with oxidation of the amino acid to an imino acid. Non-enzymatic hydrolysis at the imine centre leads to the elimination of ammonia and formation of an alpha-ketoacid. The mechanism is thought to involve a base for the abstraction of a proton from the amino group of the substrate and subsequent transfer of a hydride from the alpha carbon to the N5 of the isoalloxazine ring of FAD to form the imino intermediate.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    His P81382 241 1f8r 223
    Lys P81382 344 1f8r 326
    Step Components

    overall reactant used, proton transfer, overall product formed, bimolecular nucleophilic addition, native state of cofactor regenerated, intermediate formation, aromatic bimolecular nucleophilic addition, hydride transfer, elimination (not covered by the Ingold mechanisms)

    Step 1.

    His223 acts as a base to deprotonate the amine group of the amino acid substrate.

    Step 2.

    Once depronated the substrate is activated for hydride transfer from the alpha-C atom to the N5 of FAD, forming the imine intermediate.

    Step 3.

    The presence of a structurally conserved water molecule and lysine residue suggest a possible role for Lys326 in activating the water for hydrolysis of the intermediate. The intermediate is subject to nucleophilic attack by the water, while the imine accepts a proton.

    Step 4.

    In an inferred hydrolysis step there is movement of electrons from the hydroxyl lone pair, causing elimination of ammonia and forming the product. Following hydrolysis there is an oxidative half reaction in which the cofactor FADH- is reoxidised to FAD by molecular oxygen.


    The products of the reaction.

Reaction Parameters

There are no kinetic parameters information for this Enzyme

Associated Proteins

Protein name Organism
L-amino acid oxidase Bs29 Eyelash palm pitviper
Putative L-amino-acid oxidase YobN Bacillus subtilis (strain 168)
L-amino-acid oxidase L2 Russel's viper
L-amino acid oxidase Cdc18 South American rattlesnake
L-amino-acid oxidase Mouse