Lysine 183 is the general base in the 6-phosphogluconate dehydrogenase-catalyzed reaction

Site-directed mutagenesis was used to change K183 of sheep liver B-phosphog luconate dehydrogenase to A, E, H, C, Q, R, and M to probe its possible rol e as a general base catalyst. Each of the mutant proteins was characterized with respect to its kinetic parameters at pH 7 and the pH dependence of ki netic parameters for the K183R mutant enzyme. The only mutant enzyme that g ives a significant amount of catalysis is the K183R mutant, and the extent of catalysis is decreased by about 3 orders of magnitude; the general base pK is perturbed to a pH value of >9. All other mutant enzymes exhibit rates that are decreased by about 4 orders of magnitude compared to that of the wild-type enzyme. Data are consistent with the general base function of K18 3.