ABSTRACT
I. Introduction ...................................................................................................................... 861
II. Theory .............................................................................................................................. 862
III. Examples .......................................................................................................................... 866
A. Cytochrome P450..................................................................................................... 866
B. The Aromatic Amino Acid Hydroxylases............................................................... 868
C. Dopamine b-Monooxygenase.................................................................................. 870
IV. Conclusion........................................................................................................................ 871
References..................................................................................................................................... 871
As discussed elsewhere in this volume, substitution with a heavier isotope of an atom in the
substrate for an enzyme-catalyzed reaction will not necessarily result in a detectable change in
either the rate of product formation in a single assay or on the V
and V/K values determined from
more complete kinetic analyses. Expression of intrinsic isotope effects on V
values can be
masked by slower chemical steps steps which are not isotope-sensitive and by slow product release,
while effects on V/K values can be masked by high commitments to catalysis.
