Two-step reaction mechanism reveals new antioxidant capability of cysteine disulfides against hydroxyl radical attack

Abstract

Significance In this work, we harnessed mass spectrometry for online reaction monitoring of hydroxyl radical ( • OH) attack to cysteine disulfide and acquired mechanistic details that had not been achieved previously. Our findings suggest that • OH substitution at the disulfide bond is a fast and predominant reaction channel in the gas phase, while subsequent hydrogen transfer within the product pairs can be favorable in protonated systems. Notably, by reacting with • OH cysteine disulfide converts itself to a more potent antioxidant, sulfenic acid (–SOH), thus forming two lines of defense against reactive oxygen species (ROS). These results provide insight into studying the antioxidant roles of cysteine disulfide in nonpolar biological environment, such as at the interface of lipid membrane and plasma.