The Chemistry of Thiol Oxidation and Detection

The thiol functional group of the amino acid cysteine can undergo a wide array of oxidative modifications and perform a countless number of physiological functions. In addition to forming covalent cross-links that stabilize protein structure and functioning as a powerful nucleophile in many enzyme active sites, cysteine appears to be the principal actor in redox signaling, functioning as a regulatory reversible molecular switch. It is increasingly appreciated that the thiol group of cysteine in subset of proteins undergoes oxidative modification in response to changes in the intracellular redox environment. To understand these complex but critical biological phenomena, the chemistry of the thiol functionality and related oxidation products must also be taken into consideration. Selective methods to monitor and quantify discrete cysteine modifications will be central to understanding their regulatory and pathophysiologic function. Accordingly, this chapter focuses on the chemical feature of thiol oxidation and on selective methods for detecting oxidants and individual cysteine chemotypes.