Redox regulation of protein tyrosine phosphatases: methods for kinetic analysis of covalent enzyme inactivation.

Phosphorylation of tyrosine residues is an important posttranslational modification that modulates the function of proteins involved in many important cell signaling pathways. Protein tyrosine kinases and protein tyrosine phosphatases (PTPs) work in tandem to control the phosphorylation status of target proteins. Not surprisingly, the activity of some PTPs is regulated as part of the endogenous cellular mechanisms for controlling the intensity and duration of responses to various stimuli. One important mechanism for the regulation of PTPs involves endogenous production of hydrogen peroxide (H2O2) that inactivates enzymes via covalent modification of an active site cysteine thiolate group. Other endogenous metabolites and xenobiotics that inactivate PTPs via covalent mechanisms also have the potential to modulate signal transduction pathways and may possess either therapeutic or toxic properties. This chapter discusses methods for quantitative kinetic analysis of covalent inactivation of PTPs by small molecules.