Sandbox Reserved 967: Difference between revisions
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The hydrolysis can be decomposed in 3 steps: | The hydrolysis can be decomposed in 3 steps: | ||
* '''1''' : Deprotonation of a water molecule coordinated to the metal MB++ to form a nucleophile OH- ion. This hydroxide ion will then be properly oriented for an in-line nucleophilic attack of the target phosphate. The deprotonation mechanism has not been elucidated yet but two hypothesis can explain this step. According the first one, the metal MB++ might be responsible for the generation of water nucleophile. The other one involve a participation of the pro-R oxygen of the phosphate immediately to the 3’ side of the scissile bond, which is likely to serve as a general base for deprotonation (with transfer of the H+ to the solvent).This pro-R oxygen is also thought to play a role in the proper orientation of the hydroxide ion. | * '''1''' : Deprotonation of a water molecule coordinated to the metal MB++ to form a nucleophile OH- ion. This hydroxide ion will then be properly oriented for an in-line nucleophilic attack of the target phosphate. The deprotonation mechanism has not been elucidated yet but two hypothesis can explain this step. According the first one, the metal MB++ might be responsible for the generation of water nucleophile. The other one involve a participation of the pro-R oxygen of the phosphate immediately to the 3’ side of the scissile bond, which is likely to serve as a general base for deprotonation (with transfer of the H+ to the solvent).This pro-R oxygen is also thought to play a role in the proper orientation of the hydroxide ion. | ||
* '''2''' : In line attack by hydroxide ion of the target phosphate. During this step, a pentacovalent phosphate (transition state) is formed and stabilized by metal MA++. The metal MA++ interacts with both the nonbridging and 3' bridging oxygen | * '''2''' : In line attack by hydroxide ion of the target phosphate. During this step, a pentacovalent phosphate (transition state) is formed and stabilized by metal MA++. The metal MA++ interacts with both the nonbridging and 3' bridging oxygen and the strain induced by this double briding is thought to accelerate the hydrolysis rate. This step release a 3’ oxyanion stabilized by metal MA++ acting as a Lewis acid. | ||
* '''3''' : The cleaved phosphate cannot simultaneously coordinate the two metal ions anymore, and likely one of the metal ions leave the active site which triggers a release of cleave product. | * '''3''' : The cleaved phosphate cannot simultaneously coordinate the two metal ions anymore, and likely one of the metal ions leave the active site which triggers a release of cleave product. | ||
