Enolase Information

Elmination Reaction. The phosphate has already been placed on C₂ of glycerate from the previous enzyme.

The Enol functional group.  
Now an elimination reaction will remove a water (hydroxyl -OH group for C₃aand a hydrogen from C₂) The result is a double bond between C₂ and C₃. Compounds that contain a carbon - carbon double bonds (C=C) are always named with an ending of -ene. For example Propane is a three carbon compound with only single bonds between carbons and all other bonds are filled by hydrogen. Propene is the same except that it contains one C=C. In the case of phosphoenolpyruvate, C₂ has this double bond to C₃ AND it also has a hydroxy group on it as well. Therefore C₂ is now named an "enol" ("en" = ene for the C=C and "ol" is for alcohol).

The significance of the Enol group
Enols are not very stable in water. Generally there is a rapid, facile, nonezymatic conversion between an enol and a ketone.This type of conversion is called tautomerization and occurs extremely quickly. Thermodynamically, the ketone form is greatly favored - therefore the ketone is in much high concentration than the enol fom.

The conversion is allowed to occur only IF the the enol has an -OH on it like compound "A" ... because the terminal -H must be able to dissociate as H⁺ for the conversion.

In phosphoENOLpyruvate the enol does not terminate with -H but with -PO₃  like compound "B"which cannot dissociate therefore the molecule is trapped in this less favorable enol form.

Thermodynamically speaking hydrolysis of phosphate from phosphoenolpyruvate has a very high favorable Standard Free Energy because two things happen... we get the hydrolysis AND then the enol converts mostly to the much more stable ketone.

Cofactors/Cosubstrates

a metal ion usually Mg²⁺ is required as a cofactor

ΔG°'

+1.8 kJ/M

Starting from standard state and allowing the reaction to come to equilibrium the 2-phosphoglycerate concentration would end up ~2 times higher than that of phosphoenolpyruvate (PEP)

The Standard Free Energy favors 2-phosphglycerate.

K_eq

Comments

"In cell" Substrate Concentrations^*

S₁ =

S₂ =

P₁ =

P₂ =

ΔG for these conditions

+1.1 kJ/M

Mechanism for Chemistry

Mechanism for Enzyme

Picture of Enzyme with substrate

1. RibbonsEnolase in ribbons diagram
2. Ribbons + Mg The Mg²⁺ ion is displayerd as a green sphere
3. Ribbons + Mg + 2-P-Glycerrate2-Phosphoglycerate is added
4. Nearby AAThe amino acid sidechains near the Mg ion are added.
5. remove ribbonsSame as above with protein ribbons removed
6. rotation to demonstate orientationThe active site amino acids and substrates are rotated to demonstate their orientation