In contrast to previous studies that have shown that the neutral phenol serves as the nucleophile for WT Csk-promoted phosphorylation of a tyrosine-containing substrate, the phenolate ion acts as primary nucleophile for the D314N Csk-catalyzed reaction. Rate comparisons of D314N Csk-promoted phosphotransfer using a series of fluorotyrosine-containing peptide substrates reveal a near zero beta(nuc), consistent with a dissociative mechanism of phosphotransfer. These combined results argue against a hydroxy nucleophile-to-phosphate proton transfer occurring prior to an associative transition state of phosphoryl transfer.
Williams, D. M., & Cole, P. A. (2002). Proton demand inversion in a mutant protein tyrosine kinase reaction. Journal of the American Chemical Society, 124(21), 5956–5957. https://doi.org/10.1021/ja025993a