Many nuclear proteins contain thiols, which undergo reversible oxidation and are critical for normal function. These proteins include enzymes, transport machinery, structural proteins, and transcription factors with conserved cysteine in zinc fingers and DNA-binding domains. Uncontrolled oxidation of these thiols causes dysfunction, and two major thiol-dependent antioxidant systems provided protection. The redox states of these systems, including the small redox active protein thioredoxin-1 (Trx1) and the abundant, low molecular weight thiol antioxidant glutathione (GSH), in nuclei provide means to quantify nuclear redox conditions. Redox measurements are obtained under conditions with excess thiol-reactive reagents. Here we describe a suite of methods to measure nuclear redox state, which include a redox Western blot technique to quantify the redox state of Trx l, a biotinylated iodoacetamide (BIAM) method for thioredoxin reductase-1 (TrxR1), GSH redox measurement using total protein S-glutathionylation, and a redox isotope-coded affinity tag (ICAT) method for measuring oxidation of specific cysteines in high-abundance nuclear proteins.
