Kinetics of absorption of CO 2 into buffer solutions containing carbonic anhydrase

Abstract

The rate of absorption of pure CO 2 into equimolar phosphate (pH = 6.6 and 1 1) and carbonate (pH ≈ 9.6) buffers in the presence of crude carbonic anhydrase has been measured in a stirred cell at a temperature range of 5-35°C and at atmospheric pressure. Some experiments with carbonate buffer were also repeated in a wetted wall column. Experimental results were analysed using classical gas absorption with chemical reaction theory in order to extract information about the kinetics of the enzymic hydration of CO 2 and the catalytic power of carbonic anhydrase. At high pH-values (9.6-11.1) this reaction is first order in CO 2 the reaction rate constant being proportional to enzyme concentration with a rate constant of about 0.90 1/mg sec at 25°C and with an activation energy of 9.0 kcal/g mole. At low pH-values (pH ≈ 6.5-6.7) the catalytic power of the enzyme is considerably reduced and the results are not compatible with a simple first order reaction mechanism.