Effect of Carbonic Anhydrase on the Activity of Ribulose Bisphosphate Carboxylase

At concentrations of CO₂ less than saturating, carbonic anhydrase(EC 4.2.1.1 EC] ) stimulates the carboxylation of ribulose bisphosphatecatalysed by ribulose bisphosphale carboxylase (EC 4.1.1.3 EC] .9)in vitro. This is not through any beneficial association ofthe two enzymes but is a consequence of the increased rate ofconversion of HCO₃^– ion to CO₂, the substrate for thecarboxylation. Carbonic anhydrase should always be includedin reaction mixtures used to determine the Michaelis constantof ribulose bisphosphate carboxylase for CO₂ where fixationof radioactive CO₂ into phosphoglycerate is the basis of rateestimation. The effect is to decrease the value obtained forthe Michaelis constant.