EC Number   |
Natural Substrates |
|---|
   1.13.12.15 | aromatic amine + 1/2 O2 |
oxidative deamination, unusual oxygen-consuming reaction catalyzed by the enzyme toward aromatic amines (serotonin, dopamine, and alpha-methyldopamine) and D-tryptophan methyl ester |
| 1.13.12.15 | D-tryptophan methyl ester + 1/2 O2 |
production depending on the nature of the substrate, and ammonia with concomitant O2 consumption in a 1:2 molar ratio with respect to the products |
| 1.13.12.15 | L-DOPA + O2 |
- |
| 1.13.12.15 | more |
The novelty in DDC is the possibility of catalyzing a reaction involving dioxygen although the enzyme lacks of any cofactor or metal related to O2 chemistry. The external aldimine intermediate undergoes a decarboxylation or a deprotonation leading to a quinonoid species, that is protonated at C4 producing the ketimine intermediate. Although it cannot be ruled out that this intermediate could be attacked by dioxygen, it seems much more likely, regarding enzymes proceeding through a carbanion chemistry on DDC, that the more electron dense quinonoid intermediate, in equilibrium with the ketimine, is reactive toward O2. Aerobiosis shifts the quinonoid-ketimine equilibrium toward quinonoid, while anaerobiosis shifts the equilibrium toward ketimine. The reaction between dioxygen and the quinonoid give rise directly to a superoxide anion and semiquinone. Superoxide is deprotonated and its anionic form is thus able to couple with the semiquinone giving rise to a peroxide species that is further protonated, and thus forming a hydroperoxy-pyridoxal 5'-phosphate intermediate. This rearranges to produce aldehyde, ammonia and hydrogen peroxide. |
