Enolase

Enolase, also known as phosphopyruvate hydratase, catalysis the conversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP). This is the penultimate step of glycolysis.

Chemical equation

$2PG \rightleftharpoons PEP$

Rate equation

Mono-substrate reversible Michaelis-Menten equation is used.

$\frac{V_{mf}\frac{[2PG]}{K_{2PG}}-V_{mr}\frac{[PEP]}{K_{PEP}}}{1 + \frac{[2PG]}{K_{2PG}} + \frac{[PEP]}{K_{PEP}}}$

Modified rate law to take Thermodynamic constraint into consideration

$\frac{V_{mf}\frac{[2PG]}{K_{2PG}} \left( 1 -\frac{[PEP]}{K_{eq} [2PG]} \right)}{1 + \frac{[2PG]}{K_{2PG}} + \frac{[PEP]}{K_{PEP}}}$

Parameter values

Parameter	Value	Units	Organism	Remarks
$V_{mf}$	0.34	$\text{mM min}^{-1}$	HeLa cell line
$V_{mr}$	0.38	$\text{mM min}^{-1}$
$Km_{2PG}$	0.038	mM
$Km_{PEP}$	0.06	mM

Parameters with uncertainty

• Three values for $Km_{2PG}$ is collected. The values are 0.20 , 0.199 , 0.038 . The mean and std. dev. is $0.145 \pm 0.07$

• Similarly for $Km_{PEP}$ three reported values are 0.58, 0.702, 0.06. The uncertainty is then $0.44 \pm 0.276$.

• In Pietkiewicz et. al. (2009) $V_{mr}$ is reported as 1.4 $mmol/min^{-1}$ and Marín-Hernández et. al. (2011) reported it to be 0.4. The mean and the std. dev. calculated from these two values are $0.9 \pm 0.5$.

Parameter	Value	Units	Organism	Remarks
$V_{mf}$	$0.36 \pm 0.15 (5)$ $23.4 \pm 9.75$	$U\cdot(\text{mg protein})^{-1}$ $\text{mM min}^{-1}$	HeLa cell line
$V_{mr}$	$0.9 \pm 0.5$	$\text{mM min}^{-1}$
$Km_{2PG}$	$0.145 \pm 0.07$	mM	Human muscle
$Km_{PEP}$	$0.44 \pm 0.276$	mM	Human muscle

Equilibrium constant

Equilibrium constant	Conditions	Source
3.6	pH=7, T=25°C	Voet et al. from Newshole et al. (1973) p 97: $\Delta G' = -3.2\ kJ.mol^{-1}$, $Keq = exp(-\frac{\Delta G'}{RT}) = exp(\frac{3200}{8.31*298.15}) \approx 3.6$
6.7	T=25°C	Bergmeyer Methods of enzymatic analysis page 449
2.03	pH=7, T=297.15 K	From Meyerhof et al. (1947): $\Delta G' = -1.757\ kJ.mol^{-1}$, $Keq = exp(-\frac{\Delta G'}{RT}) = exp(\frac{1757}{8.31*298.15}) \approx 2.03$
4.29	pH=7, T=298.15 K, c(MgSO4,mol dm-3) =0.001	From Wold et al. (1957) (NIST database [57WOL/BAL_1173])
3.92	pH=7, T=298.15 K, c(MgSO4,mol dm-3) =0.01	From Wold et al. (1957) (NIST database [57WOL/BAL_1173])

• Taking average from these values give $4.1 \pm 1.68$