Thiols attached to rat liver non-histone nuclear proteins.

Up to 88% of the total thiol present in isolated rat liver nuclei can be extracted with 8 M urea 50 mM phosphate pH 7.6. There is approx. 5–10% disulphide material present in this extract. When the thiols were labelled with ¹⁴C-N-ethyl maleimide (¹⁴C-NEM) the thiol material co-electrophoresed with the protein material. If a mixed disulphide was formed with ³⁵S-labelled 5-thio-2-nitrobenzoic acid (Ellman's reagent) the thiol compounds could be removed from the protein by isoelectric focusing in polyacrylamide gel. The mixed disulphides obtained could be resolved into at least 10 components on DEAE cellulose. One of the major components had an estimated molecular weight of 3 000 and did not contain peptide material.