Quantification of the Redox State of Protein Disulfide Bonds.

To elucidate how a functional disulfide bond controls protein activity, it is essential that the redox state of the bond in the population of protein molecules is known. A differential cysteine alkylation and mass spectrometry technique is described that affords precise quantification of protein disulfide bond redox state. The utility of the technique is demonstrated by quantifying the redox states of the eight disulfide bonds in human coagulation factor VIII.