UDPG-pyrophosphorylase

This enzyme converts UTP and G1P to UDP-glucose (UDPG) and pyrophosphate (PPi)

Chemical equation

$UTP + Glc1P \leftrightarrow UDPG + PPi$

Rate equation

Reversible Bi substrate Michaelis-Menten equation with random binding order is used

$\frac{ \frac{V_{max}}{K_{UTP}K_{Glc1P}} \left( [UTP][Glc1P] - \frac{[UDPG][PPi]}{K_{eq}} \right) }{ \left( 1 + \frac{[UTP]}{K_{UTP}} + \frac{[PPi]}{K_{PPi}} \right) \left( 1 + \frac{[UDPG]}{K_{UDPG}} + \frac{[Glc1P]}{K_{Glc1P}} \right) }$

Parameter values

Parameter	Value	Units	Organism	Remarks
$V_{max}$	200	$min^{-1}$	Recombinant, human muscle
$K_{Glc1P}$	0.4	mM
$K_{UTP}$	0.92	mM
$K_{UDPG}$	$6.3 \times 10^{-2}$	mM
$K_{ppi}$	$0.38$	mM
$K_{eq}$	$0.24$	Dimensionless

Parameters with uncertainty

• The value of $V_{max}$ is reported to be $9.6 %$ of $V_{max, PGLM}$. The Std. Dev. for $V_{max, PGLM}$ was considered to be $10.5%$ of its mean value. Same error percentage is considered for $V_{max}$.

Parameter	Value	Units	Organism	Remarks
$V_{max}$	$200 \pm 21$	$min^{-1}$	Recombinant, human muscle
$K_{Glc1P}$	$0.4 \pm 0.051$	mM
$K_{UTP}$	$0.97 \pm 0.08$	mM
$K_{UDPG}$	$0.063 \pm 0.006$	mM
$K_{ppi}$	$0.38 \pm 0.036$	mM
$K_{eq}$	$0.20 \pm 0.08$	Dimensionless

Equilibrium constant

Equilibrium constant	Conditions	Source
$0.20 \pm 0.08$	pH=7 and 7.9, T=25°C, 10mM Mg2+	NIST database "Thermodynamics of Enzyme-Catalyzed Reactions" entry [[1]] from Atkinson et al. (1958) reported 4 values for Keq; 0.119, 0.286, 0.139, 0.263. Taking mean and std. for these values give $K_{eq} = 0.20 \pm 0.08$(n=4).