Biochemical and Biophysical Research Communications

Kinetic parameters of human carbonic anhydrase B as determined from NMR linewidths of 13C in CO2 and HCO3-

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The linewidths of the 13C NMR signals of CO2 and HCO3-, in equilibrium aqueous solutions containing small amounts of carbonic anhydrase, are determined mainly by the rate of enzyme-induced interconversion of CO2 and HCO3-. We have measured these linewidths in unbuffered solutions of human carbonic anhydrase B for several values of [CO2], at 25°C as a function of pH. From a least-squares analysis of the data, using the equations relating the linewidths to the enzyme kinetics, we have obtained values for the kinetic (Michaelis-Menten) parameters that characterize this interconversion. These preliminary results are in approximate agreement with published values for highly buffered solutions. Additionally, the results confirm that the product of the hydration reaction, and the substrate for the dehydration, is the neutral molecule H2CO3. © 1973.