Dynamic evidence for metal ion catalysis in the reaction mediated by a flap endonuclease
Author(s) -
Tock Mark R.,
Frary Elaine,
Sayers Jon R.,
Grasby Jane A.
Publication year - 2003
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/cdg098
Subject(s) - library science , chemistry , computer science
On the basis of structural work, metal ions are proposed to play a catalytic role in reactions mediated by many phosphoryl transfer enzymes. To gain dynamic support for such mechanisms, the role of metal ion cofactors in phosphate diester hydrolysis catalysed by a flap endonuclease has been studied. The pH maximal rate profiles were measured in the presence of various metal ion cofactors; in each case, a single ionic form of the enzyme/cofactor accounts for the pH dependence. The kinetic p K a s display good correlation with the acidity of the corresponding hexahydrated metal ions, which strongly suggests a role for metal‐bound hydroxide, or its equivalent ionic species, in the reaction. Comparing rates of reaction in the pH‐independent regions, a small negative β nuc value is observed. This suggests that expected trends in the nucleophilicity of the various metal‐bound hydroxides are balanced by a second form of metal ion catalysis that is related to the acidity of the hexahydrated metal ion. This is likely to be either electrophilic catalysis or leaving group activation.