Entry M0144    arsenite oxidase

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Step 03

An unidentified base activates water to attack the Mo(IV), forming a hydroxide group in place of the lost oxo group in a nucleophilic addition to the Mo(IV).

GIF of Reaction Step M0144.stg03

Comment: The most likely explanation for the transfer of two protons upon electrochemical oxidation without the presence of a pK transition over the range of pH 5-10 is that they are derived from an uncoordinated water in the Mo(IV) state, leaving an unprotonated oxo in the Mo(VI) state [3]. There is also evidence that under single-turnover conditions in [18-O] water, 18-O is incorporated into the molybdenum centre as a terminal oxo (Mo=O) group [1].


Proton Transfer
Bimolecular Nucleophilic Addition

Mechanism Components

Bond Formation
Metal Coordination
Bond Cleavage
Bond Order Change
Intermediate Formation
Overall Product Formed

Amino acids involved in the reaction step.

Amino Acid Location of Function Activity Function
Ser238 Main Chain Carbonyl spectator Hydrogen Bond Acceptor
Cys24 Side Chain spectator Metal Ligand
Ser99 Main Chain Amide spectator Hydrogen Bond Donor
Ser98 Main Chain Carbonyl spectator Hydrogen Bond Acceptor
His62B Side Chain spectator Hydrogen Bond Donor
Metal Ligand
His81B Side Chain spectator Metal Ligand

Organic Cofactors involved in the reaction step

Cofactor Type Cofactor Activity Function
Molybdopterin guanosine dinucleotide MGD5002 spectator Metal Ligand

Metal Cofactors involved in Step 03

Metal Type Metal Identity Chain Activity Function
molybdenum 4MO 5004 x spectator Substrate Binding
Increase Acidity
iron FS3 5005 x spectator Not Active
iron FES 5006 x spectator Not Active

Reactive Centre

Bonds Formed Bonds Cleaved Bonds Changed in Order Atom Types Involved
The Mo-O bond changes from a triple to double bond

View similar reactions in MACiE.