No abstract

Protein thiol groups that are buried often react slowly with Ellman's reagent [5,5'-dithiobis(2-nitrobenzoic acid)], ESSE. The site at which these thiol groups reside may be studied kinetically by using mixtures of ESSE and another disulfide, RSSR, which does not produce a chromophore. If RSSR competes successfully for the protein thiol group, the RSH generated reacts with ESSE to produce ES-. The rate of reaction of a variety of disulfides with the protein may be determined. This method was applied to bovine serum albumin, BSA, and a large variation in rate was found, depending upon the structure of the disulfide. After appropriate corrections for the inherent reactivity of the disulfide, a clear picture of the favorabilitv of the interaction of the R group on RSSR with the thiol site arose. The data for BSA suggest that the thiol sits in a constricted hydrophobic site. A /3-amino group on the disulfide increases the rate, presumably by an internal ion pair formation. The physiological role of the thiol function is apparently not to react with the cystine or oxidized glutathione.

No abstract