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  • Title: Spin labeling of protein sulfhydryl groups by spin trapping a sulfur radical: application to bovine serum albumin and myosin.
    Author: Graceffa P.
    Journal: Arch Biochem Biophys; 1983 Sep; 225(2):802-8. PubMed ID: 6312894.
    Abstract:
    Reaction of sulfhydryl-containing compounds, RSH, with Ce4+ in the presence of the spin trap phenyl-N-t-butylnitrone results in the appearance of a nitroxide ESR spectrum, which is greatly diminished if the sulfhydryl group is blocked prior to reaction. The spectra have short lifetimes which can be increased two- to fivefold to half-lives of 5-60 min by prior flushing of the solutions with nitrogen. For small molecules, such as cysteine, N-acetylcysteine, glutathione, and 2-mercaptoethanol, the spectrum is that of a freely rotating nitroxide while for the proteins, bovine serum albumin and myosin, the spectrum is characteristic of a strongly immobilized nitroxide spin label rigidly attached to the protein. Since Ce4+ is reported to oxidize the sulfhydryl group via the thiyl radical, RS, the following reactions are proposed to account for the formation of the nitroxide: (formula; see text) These reactions permit the spin labeling of sulfhydryl proteins such that the nitroxide is much closer to the point of attachment than when using conventional spin-labeling methods.
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