Limits on the expression of enzyme-mediated solvent isotope effects

Journal Article · Wed Mar 11 04:00:00 EST 1981 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00395a035· OSTI ID:6520550

Northrop, D B

Steady-state analysis of primary solvent isotope effects on enzyme-catalyzed reactions, mediated by solvent-shielded di- or triprotic groups on the enzyme, yields equations describing the upper limit of intramolecular isotopic discrimation. For diprotic groups (P/sub H)/(P/sub D/) = 3k/sub H//k/sub D/ + 3), and for triprotic groups (P/sub H/)/(P/sub D/) = (7(k/sub H//k/sub D//sup 2/ = 10k/sub H/k/sub D/ + 1)/((k/sub H//k/sub D/)/sup 2/ + 10k/sub H//k/sub D/ + 7). Given a normal intrinsic isotope effect of k/sub H//k/sub D/ = 7, maximal isotopic discrimation in 50:50 H/sub 2/O:D/sub 2/O is therefore 2.2 and 3.3, respectively, versus 1.0 for a monoprotic group. Intermediate values of isotope discrimination may be interpreted with respect to distinguishing enzyme-mediated catalytic mechanisms from those of direct transfer between solvent and substrate, and to identifying mediating groups, by comparisons of isotopic discrimination at high and low concentrations of substrates and by reference to intrinsic and intermolecular isotope effects.

• Research Organization: Univ. of Wisconsin, Madison
• OSTI ID: 6520550
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 103:5; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
CATALYTIC EFFECTS
DATA
DEUTERIUM
ENZYMES
HEAVY WATER
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
INFORMATION
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
OXYGEN COMPOUNDS
STABLE ISOTOPES
THEORETICAL DATA
WATER