Date of Award
Restricted Access Dissertation
Doctor of Philosophy
Field of Study
Graduate School of Biomedical Sciences
Stephen R. Grant
Price, Nancy E., Mechanistic Studies of the Sheep Liver 6-Phosphogluconate Dehydrogenase and cDNA Cloning. Doctor of Philosophy (Biomedical Sciences), July, 1996, 124 pp., 5 tables, 28 Figures, 2 appendices, bibliography, 45 titles. A kinetic characterization of sheep liver 6-phosphogluconate dehydrogenase including product and dead-end inhibition patterns, primary deuterium isotope effects, and the pH dependence of kinetic parameters has been completed in order to determine the kinetic mechanism, and chemical mechanism of the enzyme. A rapid equilibrium random kinetic mechanism has been proposed, with product and dead-end inhibition patterns both being symmetric. Primary deuterium isotope effects were equal on V and V/K, confirming a rapid equilibrium mechanism, and indicate that hydride transfer is at least partially rate limiting in the overall reaction. The maximum velocity is pH dependent, decreasing at low and high pH with slopes of 1 and -1, respectively. The V/KNADP and V/K6PG also decrease at low and high pH with slopes of 1 and -1. The pH rate profiles are consistent with a general acid/general base mechanism where the catalytic residues are involved in binding. Reverse protonation states between the general acid and the general base is proposed where an unprotonated general base accepts a proton from the C-3 hydroxyl of 6PG concomitant with hydride transfer followed by decarboxylation of the resulting 3-keto intermediate to give an enediol which is protonated by the general acid to form ribulose-5-phosphate. The pH dependence of the pKi profile of the inhibitory analog 5-phosphoribonate decreases at low and high pH with slopes of 1, and -1 respectively, and suggests that intrinsic pKs are observed in the V/K profiles. The pKs of both the general base and general acid in the E:6PG complex appears to be perturbed such that the general base pK decreases slightly, and the pK of the general acid increases slightly, as a result of direct interaction with 6PG. Additionally, in preparation for site-directed mutagenesis, cDNA clones for sheep liver 6PHDH were obtained by RT-PCR.
Price, N. E.
"Mechanistic Studies of the Sheep Liver 6-Phosphogluconate Dehydrogenase and cDNA Cloning" Fort Worth, Tx: University of North Texas Health Science Center;