Concerted transition model limitations

Scheme 5 A model for the mechanism of the phosphotriesterase reaction. The data do not clearly distinguish between a concerted mechanism of phosphoryl transfer, or a phosphorane intermediate in the model above the reaction is shown as a concerted process. In either case, the P-OLg bond is largely broken in the transition state, requiring that breakdown of any putative intermediate is rate-limiting for less activated substrates. For more labile substrates, such as paraoxon, a step involving proton transfer that occurs after phosphoryl transfer is rate-limiting.

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