Hexose-6-phosphate isomerase

The enzyme Hexose-6-phosphate isomerase converts Glucose 6-phosphate (Glc6P) into its isomer Fructose 6-phosphate (Fru6P). Isomers have the same molecular formula, but the atoms of each molecule are arranged differently.

Chemical reaction

$Glc6P \rightleftharpoons Fru6P$

Rate equation

Reversible competitive inhibition with Ery4P, 6PG and FBP.

Failed to parse (Cannot store math image on filesystem.): \frac{V_{mf}\frac{[Glc6P]}{Km_{Glc6P}} - V_{mr} \frac{[Fru6P]}{Km_{Fru6P}} }{ 1 + \frac{[Glc6P]}{Km_{Glc6P}} + \frac{[Fru6P]}{Km_{Fru6P}} + \frac{[ERY4P]}{Ki_{ERY4P}} + \frac{[6PG]}{Ki_{6PG}} + \frac{[Fru1,6BP]}{Ki_{Fru1,6BP}} }

Substituting with Haldane equation to ensure thermodynamic consistency we have

Failed to parse (syntax error): V_{mf}\frac{\left(1 - \frac{[Fru6P]}{K_{eq}[Glc6P]} }{ 1 + \frac{[Glc6P]}{Km_{Glc6P}} + \frac{[Fru6P]}{Km_{Fru6P}} + \frac{[ERY4P]}{Ki_{ERY4P}} + \frac{[6PG]}{Ki_{6PG}} + \frac{[Fru1,6BP]}{Ki_{Fru1,6BP}} }

Parameter values

Parameter	Value	Units	Organism	Remarks
$V_{mf}$	0.4	$mM \times min^{-1}$	HeLa cell line	3 cell assays
$V_{mr}$	0.9	$mM \times min^{-1}$		1 cell assay
$Km_{Glc6P}$	0.4 $\pm$ 0.03 mM	mM		3 cell assays
$Km_{Fru6P}$	0.05	mM		2 cell assays
$Ki_{ERY4P}$	0.001	mM		Adjusted in the interval based on activity
$Ki_{Fru1,6BP}$	0.06	mM		Adjusted in the interval based on activity
$Ki_{6PG}$	0.015	mM		Adjusted in the interval based on activity

Parameters with uncertainty

• The uncertainty of $V_{mr}$ and $Km_{Fru6P}$ for HeLa cell line are calculated based on the same proportion of uncertainty for AS-30D cell reported in the paper Marín-Hernández et. al., Modeling cancer glycolysis .

• The value of $Ki_{Ery4P}$, $Ki_{Fru1,6BP}$ and $Ki_{6PG}$ are the averaged from the forward and reverse reaction value listed in Table S6 .

• The uncertainty for $Ki_{Ery4P}$ in HeLa cell line is mentioned in the forward reaction as $1 \pm 0.07 \mu M$ and in the reverse direction as $0.86 \mu M$. The mean value is calcualated as $\frac{1 + 0.86}{2} \mu M$ and the standard deviation is calculated based on the same ratio mentioned in forward reaction which comes as $0.00093 \pm 0.000063$ in mM.

• Same principle is used for $Ki_{6PG}$. The mean value is $\frac{0.0176+0.0155}{2} = 0.017$ and the standard deviation is calculted based on the same ratio of reverse reaction for HeLa cell line; 0.0043

• There are two reported value for $Ki_{Fru1,6BP}$; 0.1, 0.06. The mean and standard deviation are calcualted from these two values.

Parameter	Value	Units
$V_{mf}$	$1.2 \pm 0.2$	$mM \times min^{-1}$
$V_{mr}$	Failed to parse (Cannot store math image on filesystem.): 2.8 \pm 0.9058	$mM \times min^{-1}$
$Km_{Glc6P}$	$0.4 \pm 0.03$ mM	mM
$Km_{Fru6P}$	$0.05 \pm 0.0214$	mM
$Ki_{ERY4P}$	$0.0009 \pm 0.000063$	mM
$Ki_{Fru1,6BP}$	$0.08 \pm 0.02$	mM
$Ki_{6PG}$	$0.017 \pm 0.0043$	mM