Solvent isotope effects and the nature of electrophilic catalysis in the action of the lactate dehydrogenase of Bacillus stearothermophilus.
Deuterium oxide at atom fractions of deuterium from 0.0 to 0.97 has an effect of less than 20% on the kinetic term kcat/KmB (believed to reflect the transition state for the hydride-transfer step) for the reduction of pyruvic acid by NADH at 55 degrees C, with catalysis by the tetrameric form of the lactate dehydrogenase of Bacillus stearothermophilus. This observation suggests that the hydride-transfer event is not assisted by protonic bridging to the carbonyl group being reduced. The results are consistent with protonic bridging only if an opposing isotope effect is present, for example from a generalized conformation or solvation change. The results are consistent with other forms of electrophilic catalysis.
Xie
M
M
Department of Chemistry, University of Kansas, Lawrence 66045-0046.
Seravalli
J
J
Huskey
W P
WP
Schowen
K B
KB
Schowen
R L
RL
D017666:Deuterium Oxide; D001411:Geobacillus stearothermophilus / Q000201:enzymology*; D007553:Isotope Labeling; D007770:L-Lactate Dehydrogenase / Q000737:chemistry / Q000378:metabolism*; D046911:Macromolecular Substances; D008433:Mathematics; D009243:NAD / Q000032:analysis; D012997:Solvents; D013056:Spectrophotometry, Ultraviolet
D046911:Macromolecular Substances; D012997:Solvents; D009243:NAD; D007770:L-Lactate Dehydrogenase; D017666:Deuterium Oxide