Interaction of Proteins with Sulfide

The addition of sodium sulfide to disulfide‐containing proteins dissolved in 0.01 N NaOH produces an absorption in the range of 320–350 nm similar to that exhibited by cystine or cystamine treated under the same conditions. Proteins free of cystine and cysteine and proteins containing disulfide bonds which have been reduced with sodium borohydride do not produce this absorbance. Urea and guanidine at 6 M concentration increase the rate of production of the absorbance while sodium dodecyl sulfate at concentration of 0.02 M has an inhibitory effect both on the rate and the extent of the absorbance. The effect of pH, concentration of reagents and of the additions of cyanide and hypotaurine has been studied. The 320–350 nm absorbance as been related to the production of persulfide groups (R‐SSH) as a result of the cleavage of disulfide bonds by sulfide. Attempts to prepare a purified model protein containing persulfide groups have failed owing to the instability of the persulfide group in conditions far from those used for its preparation.