First dehydration step Note the carbon labeled with green is the one most recently added as acetate in citrate synthase. This orientation is always the case... it never binds "upside down". The FeS cluster has an exposed iron atom at one corner. This provdides the postive charge necessary to initiate the pull on the -OH group at the middle carbon. Simultaneoulsy a base (Asparate in this case) pulls on the hydrogen ion on the adjacent carbon.

The results of the first step are shown. There is a HO- coordinated to the corner iron. and the base is protonated. The intermediate compund has a carbon-carbon double bond.

A slight rearrangement of the substrate must take place in the active site. This is a slight rotation of the intermediate relative to the FeS cluster.

The iron bound HO- attacks the carbon-carbon double bond. This causes the "extra" bond to swing out and capture the H+ from the nearby protonated amino acid.

The results of the above step are shown. The final product is shown. Note that the -OH group migrated AWAY from the most recently added acetate group. This is always the case.

Aerobic Glucose Metabolism

Aconitase Information

Enzyme Name

Aconitase

Reaction Catalyzed

two step reaction:
  1. Elimination reaction (removing the -OH on the 'middle' carbon) - results in a C=C
  2. Reverse Elimination reaction (hydration) water adds across The C=C that resulted from the first elimination. An alcohol adjacent to where it began is the result

Reaction Type

 Two Step Reaction
  1. Elimination
  2. Elimination - in reverse (hydration) but the -OH is on a different carbon

Pathway Involvement

Citric Acid Cycle

Cofactors/Cosubstrates

 The Fe/s Center is required for these eliminations. Normally, all four irons are attached to an amino acid sidechain (usually cysteine). In this case one iron is exposed to the active site.