Insights on enzymatic and uncatalyzed phosphoryl transfer.

摘要

The chemistry of phosphate monoesters forms the basis for the regulation of a host of biochemical processes, accounting in part for the intense interest in these compounds. Much of what is known about the mechanisms of phosphoryl transfer and its transition states has been suggested from experiments using aryl phosphate esters. On the other hand, most of the computational work has been performed using methyl phosphate. Thus, far less experimental data is presented on the mechanism and transition states for alkyl phosphates.; This dissertation addresses some of the key questions of uncatalyzed and enzymatic phosphoryl transfer of alkyl phosphates. The issues of solvation and medium effects were explored to deepen our knowledge about the mechanism of phosphoryl transfer in the uncatalyzed hydrolysis of aryl and alkyl phosphates.; The kinetic isotope effects were determined for reactions of hydrolysis catalyzed by alkaline phosphatase (AP), dual specificity phosphatases CdC25a and VHR, and protein tyrosine phosphatase YOP51, with meta-nitrobenzyl phosphate as a substrate. The decision was made to synthesize and use this particular compound because the pK_a value of its leaving group, m-nitrobenzyl alcohol, is very similar to that of natural phosphate monoester substrates of hydrolysis occurring in living cells where serine and threonine are phosphorylated residues. Many questions incisive for the understanding of mechanism and transition state for reactions of phosphoryl transfer with meta-nitrobenzyl phosphate were answered. This work presents comparisons of data obtained from both enzymatic as well as nonenzymatic hydrolysis of the alkyl phosphate, meta-nitrobenzyl phosphate, and aryl phosphate, para-nitrophenyl phosphate.