Difference between revisions of "Hexose-6-phosphate isomerase"

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Revision as of 10:10, 24 April 2014

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. [1]

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}} }

Parameter values

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

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 [1].
  • 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 [1].
  • The uncertainty for Ki_{Ery4P} in HeLa cell line is mentioned only in the forward reaction which is 0.07. The mean value is calcualated as Failed to parse (Cannot store math image on filesystem.): \frac{1 + 0.86}{2} and the standard deviaton is calculated based on the same ratio mentioned in forward reaction which comes as 0.0009 \pm 0.000063.
  • 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

The Xyl5P content is reported as Failed to parse (Cannot store math image on filesystem.): 0.016\pm 0.0034 [2] and Ki_{Ery4P} is reported as 0.001. The ratio is determined as 0.0625. The standard deviation then comes as 0.0002125. Same principle is used for Ki_{6PG} where first the standard deviation for 6PG in HeLa cell line is calcualted based on the error ratio of AS-30D which is Failed to parse (Cannot store math image on filesystem.): 0.39 \pm 0.144 . The standard deviation for Ki_{6PG} then comes as 0.005. There are two reported value for Ki_{Fru1,6BP}; 0.1[3], 0.06[1]. The mean and standard deviation are calcualted from these two values.

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

Refences

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 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 Cite error: Invalid <ref> tag; name "Hernandez2011" defined multiple times with different content Cite error: Invalid <ref> tag; name "Hernandez2011" defined multiple times with different content Cite error: Invalid <ref> tag; name "Hernandez2011" defined multiple times with different content
  2. ↑ L.J. Reitzer, B.M. Wice, D. Kennell (1980), The pentose cycle, J. Biol. Chem. 255 5616–5626
  3. ↑ Marin-Hernandez, A., Gallardo-Perez, J. C., Ralph, S. J., Rodriguez-Enriquez, S. & Moreno-Sanchez, R. (2009), HIF-1α modulates energy metabolism in cancer cells by inducing over-expression of specific glycolytic isoforms. Mini-Rev. Med. Chem. 9, 1084–1101
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