Detection of sulfenic acid in intact proteins by mass spectrometric techniques: application to serum samples

Abstract

Formation of cysteine sulfenic acid (SA) is considered a transient state of thiol oxidation in living organisms that can be either reduced back or continue to result in the formation of sulfinic and sulfonic acids. As any disturbance in oxidation is correlated to age-related diseases such as cancer and Alzheimer's disease, the detection of SA transient state formed a sensor for such redox-mediated events. Thus, detection of low amounts of SA is critical in order to prevent further oxidative damage of cells and tissues and for this aim specific strategies have to be developed. In this work, detection and quantification of induced SA in human serum albumin is reported by specific capture using alkyne β-ketoester (KE) previously linked to a lanthanide (Ln)-containing chelator (Ln–DOTA, where DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). SA formation was induced by hydrogen peroxide to mimic oxidative conditions produced in living cells by ROS and was detected using molecular and elemental mass spectrometric (MS) techniques. The developed strategy has been further applied to the determination of SA-induced formation in human serum by using affinity chromatography for purification of albumin followed by inductively coupled plasma mass spectrometry (ICP-MS) to monitor the formed SA linked to Ln–DOTA–KE in combination with isotope dilution analysis (IDA) for absolute quantification. Quantitative results showed levels of oxidative damage regarding SA formation in up to 40% of the albumin present.