CysQuant

CysQuant is a new method for accurately measuring the oxidation levels of cysteine residues in proteins, which is crucial for understanding protein function in redox regulation. It utilizes isotopologues of iodoacetamide to label differentially reduced and reversibly oxidized cysteines, analyzed through data-dependent acquisition (DDA) or data-independent acquisition mass spectrometry (DIA-MS). By employing plexDIA with predicted spectral libraries, the method successfully quantified cysteine oxidation in Arabidopsis thaliana, revealing both average oxidation levels and specific cysteines forming disulfide bridges. CysQuant proves to be a versatile tool applicable across different mass spectrometry platforms and organisms for assessing cysteine modification status.