Effect of Carbonic Anhydrase on the Activity of Ribulose Bisphosphate Carboxylase

Abstract
At concentrations of CO2 less than saturating, carbonic anhydrase (EC 4.2.1.1) stimulates the carboxylation of ribulose bisphosphate catalysed by ribulose bisphosphale carboxylase (EC 4.1.1.3.9) in vitro. This is not through any beneficial association of the two enzymes but is a consequence of the increased rate of conversion of HCO3 ion to CO2, the substrate for the carboxylation. Carbonic anhydrase should always be included in reaction mixtures used to determine the Michaelis constant of ribulose bisphosphate carboxylase for CO2 where fixation of radioactive CO2 into phosphoglycerate is the basis of rate estimation. The effect is to decrease the value obtained for the Michaelis constant.