Monovalent cation-induced association of formyltetrahydrofolate synthetase subunits. Solvent isotope effect

In the presence of specific monovalent cations (K+, Cs+, NH4+), inactive monomers of formyltetrahydrofolate synthetase associate to a catalytically active tetramer. The rate and extent of association of enzyme monomers prepared from C. cylindrosporum are enhanced 3.3-and about 50-fold, respectively,...

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Bibliographic Details
Published in:Biochemistry (Easton) 1975-12, Vol.14 (24), p.5379-5386
Main Authors: Harmony, Judith A. K, Himes, Richard H, Schowen, Richard L
Format: Article
Language:English
Subjects:
Ammonia
Binding Sites
Cations, Monovalent
Cesium
Clostridium - enzymology
Deuterium
Formate-Tetrahydrofolate Ligase
Kinetics
Ligases
Macromolecular Substances
Mathematics
Potassium
Protein Binding
Protein Conformation
Species Specificity
Thermodynamics
Water
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Summary:In the presence of specific monovalent cations (K+, Cs+, NH4+), inactive monomers of formyltetrahydrofolate synthetase associate to a catalytically active tetramer. The rate and extent of association of enzyme monomers prepared from C. cylindrosporum are enhanced 3.3-and about 50-fold, respectively, by the substitution of D2O for H2O. Both rate and equilibrium solvent isotope effects are due to a decrease in D2O of the dissociation constant of the monomer-cation complex. Analysis of rate and equilibria data obtained in solvent mixtures of varying deuterium/protium ratios indicates that the isotope effect may be due to the change in bonding of a single monomer proton during the association process. The data are most consistent with a model in which this proton is in a very weak potential in the cation-free monomer and is converted to a "normal" water-like proton in the monomer-cation complex.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi00695a023