Glyceraldehyde-3-Phosphate Dehydrogenase Information

Enzyme Name

Glyceraldehyde-3-Phosphate Dehydrogenase

Reaction Catalyzed

two step reaction:
In the direction of glycolysis

1. Oxidation of Glyceraldehyde-3-phosphate to glycerate-3-phosphate
2. addtion of phosphateto C₁

Reaction Type

Two Step Reaction

1. Oxidation/Redxution (REDOX)
2. Hydrolysis type reaction (with a twist here since phosphate is used to attack it is called phosphorolysis)
   

Rationale

Oxidation of an aldehyde to an acid (combined with a one slight trick). The core of this reaction is the NAD⁺ dependent oxidation of the aldehyde in glyceraldehyde to an organic acid (glycerate).

The slight trick here is that it is actually converted to the phosphoanhydride rather than a free organic acid. This can be accomplished becuase of a covalently bound intermedicate in the enzyme. This is described in much more detail in the mechanism section below.

The justification for the twist lies in thermodynamics of the next step. Remember, in one of the quiz questions, two modules ago, I indicaited that the amount of energy released from phosphoanhydride hydrolysis is MUCH higher than that for hydrolysis of a phosphate from an hydroxyl group. This extra energy is used in the next step to MAKE an ATP! (more on energy coupling later in this module).

Summing up - TWO ATP were needed to start the glycolysis pathway (hexokinase and phosphofructokinase-1) . NOW two ATP (remember there are two 3-phosphoglycerate for every glucose) are made in the following reaction... we will be back where we started in number of ATP

Pathway Involvement

Glycolysis AND gluconeogenesis

Cofactors/Cosubstrates

cosubstrates NAD⁺ and PO₄⁼ are both required in the glycolsys direction. NADH is a coproduct
          in the gluconeogenesis direction NADH is the substrate; NAD⁺and PO₄⁼ are coproducts

DG^o'

+6.3 kJ/M

Starting from standard state and allowing the reaction to come to equilibrium the substrates of glycolysis (G-3-P, PO₄ and NAD⁺) concentration would end up ~12 times higher than the product of the concetrations of 1,3 bisphosphoglycerate NADH.

The Standard Free Energy favors Fructose-1,6-bisphosphate production.

K_eq

Comments

This reaction is made possible because of two factors:

1. Coupling of the phosphate addition to the NAD⁺ linked redox
2. Formation of a required covalent enzyme bound intermediate (through a cysteine)

"In cell" Substrate Concentrations^*

S₁ =

S₂ =

P₁ =

P₂ =

NADH

0.000003 mM

DG for these conditions

-1.3 kJ/M 

Mechanism for Chemistry step one

Mechanism for Enzyme

Picture of Enzyme with substrate

1. RibbonsOnly the main chain is represented by these ribbons. There are four identical subunit
2. one subunit Three of the subunits are deleted.
3. as above with substrateSame picture as in "2" but and a substrate is added in. The atoms colored spheres. C=Gray; O=red; P=Orange.
4. nearby AA AA near the subsrate are added as sticks
5. NAD⁺ is added.
6. Ribbons removed
7. as above different orientation Active site AA + substarte + NAD but slightly different orientation to highlight the spatial orientation of the critical cysteine, NAD substrate and HIS
8. C2 of NAD= magenta HIS=vyan exactly as above but the C4 of NAD is colored magenta (this is the carbon that picks up the hydride) and the HIS is colored cyan.