Triosephosphate isomerase

This enzyme rapidly inter-converts the molecules Dihydroxyacetone phosphate (DHAP) and Glyceraldehyde 3-phosphate (Gly3P). Gly3P is removed as soon as it is formed to be used in the next step of glycolysis.

Chemical equation

$DHAP \rightleftharpoons Gly3P$

Rate equation

Reversible Michaelis-Menten is used

$v = \frac{ V_{mf}\frac{[DHAP]}{K_{DHAP}} - V_{mr}\frac{[Gly3P]}{K_{Gly3P}} }{1 + \frac{[DHAP]}{K_{DHAP}} + \frac{[Gly3P]}{K_{Gly3P}} }$

Modified rate law considering thermodynamic constant is

$v = \frac{ V_{mf}\frac{[DHAP]}{K_{DHAP}}\left(1 - \frac{[Gly3P]}{K_{eq}[DHAP]} \right)}{1 + \frac{[DHAP]}{K_{DHAP}} + \frac{[Gly3P]}{K_{Gly3P}} }$

Paramters

Parameter	Value	Units	Organism	Remarks
$V_{mf}$	5	$mM \times min^{-1}$	Hela cell line
$V_{mr}$	42	$mM \times min^{-1}$
$Km_{Gly3P}$	0.51	mM
$Km_{DHAP}$	1.6	mM

Parameters with uncertainty

• The activity is measured in Activity in the reverse reaction in Hernandez (2006) et. al. $V_{mf}$ is sampled based on Haldane equation $K_{eq} = \frac{V_{forward}*K_{product}}{V_{reverse}*K_{substrate}}$ using the value Failed to parse (Cannot store math image on filesystem.): K_{eq} = 20.9 \pm 3.1 , $Km_{Gly3P}$ and $Km_{DHAP}$. Alternatively the reported fixed point value can be considered with the standard deviation calculated based on the same ratio of $V_{mf}$ which is $\approx 31%$. This gives the value Failed to parse (Cannot store math image on filesystem.): V_{mf}=5 \pm 1.55

Parameter	Value	Units	Organism	Remarks
$V_{mf}$	Sampled based on the Haldane equation. Alternative: Failed to parse (Cannot store math image on filesystem.): 5 \pm 1.55	$mM \times min^{-1}$
$V_{mr}$	$42 \pm 13 (3)$	$mM \times min^{-1}$
$Km_{Gly3P}$	$0.40 \pm 0.03 (4)$	mM	Human liver
$Km_{DHAP}$	$0.59 \pm 0.01 (4)$	mM	Human liver
$K_{eq}$	Failed to parse (Cannot store math image on filesystem.): 20.9 \pm 3.1 (4)	mM