Treatment of CO2 in biochemical reactions

Carbon dioxide in solution does not significantly bind to hydrogen ions or other metal ions. Thus it is possible to treat CO2 as a reactant composed of a single species in biochemical reactions, without introducing a binding polynomial or multiple ion-bound states for C02. However, C02 can be hydrolyzed to H2C03 via the reaction 

For certain applications it is convenient to express apparent thermodynamic properties for reactions involving C02 in terms of total carbon dioxide, which is defined 

Alternatively, one may be interested in the apparent equilibrium properties for the biochemical reaction 

Since we have expressed [ ECXT in terms of [C032-], we must consider a reference reaction in terms of C032- rather than C02. For the biochemical reaction of Equation (2.38), we have  

An important physiological buffering system active in the blood is the bicarbonate system. Bicarbonate (H2CO3) is a weak acid that is involved in maintaining the pH of human blood in the neighborhood of 7.4. The acid-base equilibration for bicarbonate is expressed 

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We have chosen to use C032- as a reference species in reaction numbers 1, 4, and 5. Therefore the apparent thermodynamic properties of these reactions will be calculated in terms of the biochemical reactant XCO2. (See Section 2.6 for a discussion on the treatment of CO2 in biochemical reactions.)... 

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