ABSTRACT
I. Introduction ...................................................................................................................... 837
II. Theory .............................................................................................................................. 837
III. Experimental Examples ................................................................................................... 841
A. Hydrogen Tunneling ................................................................................................ 841
B. Yeast Alcohol Dehydrogenase................................................................................. 842
C. Yeast Formate Dehydrogenase ................................................................................ 844
IV. Conclusion........................................................................................................................ 844
References..................................................................................................................................... 844
Pressure can affect kinetic isotope effects (KIEs) in either of two ways: it can alter an intrinsic
isotope effect directly by perturbing transition-state (TS) phenomena, such as hydrogen tunneling,
or it can alter the expression of an otherwise stable intrinsic isotope effect by perturbing the kinetic
complexity of reactions having multiple steps, as in an enzymatic reaction. At present there are
few examples of either of the two kinds of effects, so making generalizations is rather tenuous.
Nevertheless, at this juncture it appears that both ways are accessible experimentally (below
3 kbar), both can be characterized with considerable precision when present alone, and because the
two follow different functions, it is sometimes possible to separate and characterize both when they
appear together. Indeed, the primary purpose of undertaking pressure kinetics at present is not to
find out “what happens” at high pressure, but rather to use pressure as a perturbant to deconstruct
overlapping kinetic phenomena and tease out individual components, defined in terms relating to
their occurrence at ambient pressure.
