The Kinetic Parameters of Carbonic Anhydrase by 13C Nmr

Abstract

Carbonic anhydrase, an enzyme found in red blood cells, catalyses the reversible hydration of carbon dioxide: CO2+ H2O ⇄ H++ HCO-3. We have used measurements of the 13C n.m.r. linewidths of 13CO2and H13CO─3in solutions of the native human B enzyme to obtain the kinetic parameters that describe the enzymatic activity. The measurements, made under thermal equilibrium conditions and with no added buffer, were taken as a function of pH and substrate concentration at 25°C, and at pH 7.7 over a range of temperatures. The kinetic results, which compare well with published results obtained by stopped-flow methods in buffered solutions, are discussed in terms of the several models that have been suggested to describe the enzymatic mechanism. © 1974, Walter de Gruyter. All rights reserved.