The monovalent cation-induced association of formyltetrahydrofolate synthetase subunits: a 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, 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.
D000641:Ammonia; D001665:Binding Sites; D002414:Cations, Monovalent; D002586:Cesium; D003013:Clostridium / Q000201:enzymology; D003903:Deuterium; D005574:Formate-Tetrahydrofolate Ligase; D007700:Kinetics; D008025:Ligases; D046911:Macromolecular Substances; D008433:Mathematics; D011188:Potassium; D011485:Protein Binding; D011487:Protein Conformation; D013045:Species Specificity; D013816:Thermodynamics; D014867:Water
D002414:Cations, Monovalent; D046911:Macromolecular Substances; D014867:Water; D002586:Cesium; D000641:Ammonia; D003903:Deuterium; D008025:Ligases; D005574:Formate-Tetrahydrofolate Ligase; D011188:Potassium