Pyruvate Kinase Information

Enzyme Name

Pyruvate Kinase

Reaction Catalyzed

Transfer of phosphate group from phosphenolpyruvate to ADP to make ATP and pyruvate

Reaction Type

Group Transfer Reaction

Pathway Involvement

Glycolysis ONLY

The favorable thermodynamics of the enol / ketone tautomerization (SEE RATIONALE) virtually precludes this reaction from running in the gluconeogenesis direction. Rather TWO enzymes that EACH use an ATP (or equivalent in GTP) are required to get from pyruvate to PEP in the gluconeogenesis direction

1. Pyruvate Carboxylase which makes oxaloacetate (a 4 Carbon compound) using ATP and CO₂.
2. Phosphoenolpyruvate CarboxyKinase which takes a CO₂ off of oxaloacetate and puts a phosphate on the enol using GTP (for our purposes GTP is an ATP equivalent since it serves the same function).

Cofactors/Cosubstrates

ADP along with Mg²⁺ is a required cosubstrate. ATP is a coproduct

Rationale

The Enol functional group.
Just prior to this enzyme in the pathway an elimination reaction (hydroxyl -OH group from C₃ and a hydrogen from C₂) generated a carbon-corbon double bond between C₂ and C₃. Compounds that contain a carbon - carbon double bond (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 C₂ 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 can occur extremely quickly. Thermodynamically, the ketone form is greatly favored - therefore the ketone is in much high concentration than the enol fom.

There is one caveat... 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 the 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 favorable ketone.

How much energy is in the Ketone / enol conversion. The ΔG^o' as written is +45 kJ/M which means that the ketone form is favored by a factor of ~65,000,000 over that of the enol form in pyruvate.

The extra energy from this can be used to transfer the phosphate from PEP to ADP to make ATP.

ΔG^o'

-31.7 kJ/M

K_eq

Comments

Starting from standard state and allowing the reaction to come to equilibrium the Pyruvate and ATP concentration would end up ~20,000 times higher than the product of the concetrations of ADP and PEP.

The Standard Free Energy strongly favors ATP production.

Note: the Standard Free Energy grealy favors production of ATP. (see raionale above for reasons)

This is the last of the ATPs generated in the glycolysis pathway.

1. it took two ATP (hexokinase and phosphofructokinase-1) to the the pathway started.
2. Two ATP were recovered in the glycerate kinase reaction
3. two more ATP are generated in pyruvate kinase.

recall that two 1,3 bisphosphoglycerate (this goes for PEP as well) are generated for every glucose that starts.

"In cell" Substrate Concentrations^*

S₁ =

0.031 mM

S₂ =

ADP

0.14 mM

P₁ =

Pyruvate

0.0.051 mM

P₂ =

ATP

1.85 mM

&DeltaG for these conditions

-23.0 kJ/M

Mechanism for Chemistry

Mechanism for Enzyme

Hover your mouse over a step to reveal a description

Pyruvate Kinase. Animation of the pyruvate kinase reaction Blue: represents the enzyme. "Start" begins an animation of the group transfer reaction. It proceeds through the reaction in the "forward" direction and then "backwards" again. Note how the enzyme is involved. "+" increases speed while "-" decreases the animation speed. You may also step through the reaction using "next" or "previous"

Compare the animated reaction to the "arrow pushing" scheme at the right. See if you can correlate the electron movement in the animation to the arrows in the static picture above.

Picture of Enzyme with substrate

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