Difference between revisions of "Triosephosphate isomerase"

Revision as of 14:40, 24 June 2014

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.

DHAP \rightleftharpoons Gly3P

Reversible Michaelis-Menten is used ^[1]

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}} }

Parameter	Value	Units	Organism
$V_{mf}$	5 ^[1]	$mM \times min^{-1}$	Hela cell line
$V_{mr}$	42^[2]	$mM \times min^{-1}$
$Km_{Gly3P}$	0.51^[1]	mM
$Km_{DHAP}$	1.6^[1]	mM

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
$V_{mf}$	Sampled based on the Haldane equation. Alternative: Failed to parse (Cannot store math image on filesystem.): 5 \pm 1.55	$mM \times min^{-1}$
$V_{mr}$	$42 \pm 13 (3)$ ^[2]	$mM \times min^{-1}$
$Km_{Gly3P}$	$0.40 \pm 0.03 (4)$ ^[3]	mM	Human liver
$Km_{DHAP}$	$0.59 \pm 0.01 (4)$ ^[3]	mM	Human liver
$K_{eq}$	Failed to parse (Cannot store math image on filesystem.): 20.9 \pm 3.1 (4) ^[3]	mM

Equilibrium constant	Conditions	Source
0.048	pH=7, T=25°C	Lehninger, (1975)^[4] p 553: $\Delta G' = 7.5\ kJ.mol^{-1}$ , $Keq = exp(-\frac{\Delta G'}{RT}) = exp(\frac{-7500}{8.31*298.15}) \approx 0.048$
0.51	pH=7, T=25°C	Lehninger, (2008)^[5] p 396: Keq(reverse)=1.97 => Keq(forward)=1/1.97=0.51.
0.41	pH=7, T=25°C	Voet et al.^[6] from Newshole et al. (1973) ^[7]p 97: $\Delta G' = 2.2\ kJ.mol^{-1}$ , $Keq = exp(-\frac{\Delta G'}{RT}) = exp(\frac{-2200}{8.31*298.15}) \approx 0.41$

↑ ^1.0 ^1.1 ^1.2 ^1.3 Marín-Hernández A, Gallardo-Pérez JC, Rodríguez-Enríquez S et al (2011) Modeling cancer glycolysis. Biochim Biophys Acta 1807:755–767 (doi) Cite error: Invalid <ref> tag; name "Hernandez2011" defined multiple times with different content
↑ ^2.0 ^2.1 Marín-Hernández A , Rodríguez-Enríquez S, Vital-González P A, et al. (2006). Determining and understanding the control of glycolysis in fast-growth tumor cells. Flux control by an over-expressed but strongly product-inhibited hexokinase. FEBS J., 273 , pp. 1975–1988(doi)
↑ ^3.0 ^3.1 ^3.2 Snyder, R.; Lee, E.W. (1975), Triosephosphate isomerase from human and horse liver,Methods Enzymol. 41B, 430-434
↑ David L. Nelson, Michael M. Cox (2008), Lehninger Principles of Biochemistry (5th edn), W. H. Freeman and Company
↑ Lehninger, A.L. (1975) Biochemistry (2nd edn), Worth
↑ Voet, D., Voet., J.G. and Pratt, C. W. (1999) Fundamentals of biochemistry, Wiley
↑ Newshole, E.A. and Stuart, C. (1973) Regulation in Metabolism, Wiley

@@ Line 81: / Line 81: @@
 ! Source
 |-
-| 0.50
+| 0.048
 | pH=7, T=25°C
 | Lehninger, (1975)<ref name="lehninger2008">David L. Nelson, Michael M. Cox (2008), Lehninger Principles of Biochemistry (5th edn), W. H. Freeman and Company</ref> p 553:<br/>
-<math>\Delta G' = 1.7\ kJ.mol^{-1}</math>, <math>Keq = exp(-\frac{\Delta G'}{RT}) = exp(\frac{-1700}{8.31*298.15}) \approx 0.50</math>
+<math>\Delta G' = 7.5\ kJ.mol^{-1}</math>, <math>Keq = exp(-\frac{\Delta G'}{RT}) = exp(\frac{-7500}{8.31*298.15}) \approx 0.048</math>
 |-
 | 0.51