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J Am Chem Soc. 2002 May 29;124(21):5956-7.

Proton demand inversion in a mutant protein tyrosine kinase reaction.

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Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Room 316, Hunterian Building, 725 North Wolfe Street, Baltimore, Maryland 21205, USA.


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.

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