Glutamate 190 is a general acid catalyst in the 6-phosphogluconate-dehydrogenase-catalyzed reaction.
Site-directed mutagenesis was used to change E190 of sheep liver 6-phosphogluconate dehydrogenase to A, D, H, K, Q, and R to probe its possible role as a general acid catalyst. Each of the mutant proteins was characterized with respect to the pH dependence of kinetic parameters. Mutations that eliminate a titrable group at position 190, result in pH-rate profiles with no observable pK on the basic side of the V/K6PG profile. Mutations that change the pK of the group at position 190 result in the expected pK perturbations in the V/K6PG profile. Kinetic parameters obtained at the pH optimum in the pH-rate profiles are consistent with a rate-limiting tautomerization of the 1,2-enediol of ribulose 5-phosphate consistent with the proposed role of E190. Data are also consistent with some participation of E190 in an isomerization required to form the active Michaelis complex.
Karsten
W E
WE
Department of Chemistry and Biochemistry, University of Oklahoma, Norman 73019, USA.
Chooback
L
L
Cook
P F
PF
D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D016384:Consensus Sequence; D018698:Glutamic Acid / Q000737:chemistry* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010734:Phosphogluconate Dehydrogenase / Q000737:chemistry* / Q000235:genetics; D016415:Sequence Alignment; D012756:Sheep
D018698:Glutamic Acid; D010734:Phosphogluconate Dehydrogenase