Global response coefficients

Global response coefficients, applicable to all datasets mentioned in the given script file, are listed in the [response] section. The formalism is

[response]
   A = 1.23, B = 3.45, C = 5.67

[response]
   A = 1.23
   B = 3.45
   C = 5.67

where A, B, and C are labels for chemical species appearing in the reaction mechanism.

Example 1: UV/VIS spectroscopy. Substrate S is converted to the reaction product P by a catalytic action of an enzyme. The substrate has molar absorptivity 12,000 M ${\phantom .}^{{\rm -1}}$ $\times$ cm ${\phantom .}^{{\rm -1}}$ , while the reaction product has practically zero absorption coefficient at the given wavelength. Let us assume that all concentrations in the given script file are expressed in micromolar units. Thus, 1 $\mu$ M of the substrate corresponds to 0.012 absorbance units in 1 cm cell. In this case we will write

[mechanism]
   E + S <==> ES  :   k   ks
   ES ---> E + P  :   kr
[response]
    S = 0.012
   ES = 0.012

where it is assumed that the binding of the substrate to the enzyme does not change its molar response coefficient. If the concentration of the substrate is very much larger than the concentration of the enzyme catalyst, we can ignore the absorbance due to the Michaelis complex ES and write

[mechanism]
   E + S <==> ES  :   k   ks
   ES ---> E + P  :   kr
[response]
    S = 0.012

Example 2: Polarimetry.

Michaelis & Menten (1913) followed the changes in optical rotation caused by the hydrolytic action of invertase. In their instrumental setup, one mole per liter of saccharose would cause optical rotation of +42.5 degrees, while one mole per liter of the reaction product mixture would cause optical rotation of -13.3 degrees. Assuming that all concentrations throughout the script file are expressed in millimoles per liter, we will set up the script file (neglecting the optical rotation due to the Michaelis complex) as follows:

[mechanism]
   E + S <==> ES    : k   ks    
   ES --> E + P     : kr
[responses]
   S = +0.0425
   P = -0.0133
[concentrations]
   ...

Next: Local response coefficients Up: Specific molar responses Previous: Specific molar responses Index

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Petr Kuzmic | Jul 12 2005