Enolase contains eleven b-sheet strands and twelve a-helices. Three of the b-sheet strands are located at the N-terminal end of the enzyme, as are four of the helices. The remaining helices and b-sheets form a barrel structure which is the location of the active site.

The main domain within the structure of enolase is characterized by an eight-fold b/a-barrel. (select sheets) A more accurate description of this barrel is bbaa(ba)6. (add helices) The barrel itself starts out with two b-strands, followed by two a-helices, which are then followed by six alternating b-a sequences.5 To accommodate this pattern, the first helix of the structure is in the reversed orientation, and the second b-sheet strand is antiparallel. These two chains are in the opposite orientation than than that of their corresponding structures.3

The active site is located at the carboxylic end of the barrel, which is where the metal ion cofactors (only the conformational cation is shown here) and the 2-phosphoglycerate (or, if during gluconeogenesis, the phosphoenolpyruvate) substrate binds.


The subunits of enolase are stabilized by multiple hydrogen bonds. When 2-PGA is bound at the active site, his 159 of the first subunit is typically in direct contact with the phosphoryl group of the substrate. However, the second subunit's his-159 is separated from the substrate by a water molecule.6 Thus, the first subunit is able to perform the dehydration of 2-PGA into PEP, whereas the second subunit could perform the reverse reaction if PEP was bound at the active site rather than 2-PGA. The mechanism of both these reactions is detailed on the active site page. Typically, when 2-PGA is bound at the active site, the conformation of the enzyme is considered to be "closed". When PEP and water are bound to the enzyme, and his 159 is blocked from the ligand, enolase is said to be in the "open conformation".7 Therefore, one subunit is always in the closed conformation while the other subunit is in the open conformation.


Rotation On/Off Cartoon Off/On
Hydrogen Bonds On/Off Ball & Stick/Wireframe
Spacefill Ligand site
Surface Smoothing Stereo On/Off