some Observations on the Reaction of Modified Keratins with Nitroprusside

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Abstract
The sulfhydryl groups of treated keratin differ from those of ordinary thiol compounds in their reactivity toward sodium nitroprusside—they often do not give the characteristic red-violet coloration in slightly alkaline aqueous medium. Among the several modifications of keratin investigated, only keratin treated with thio glycollate gave a positive reaction. In all other cases, however, a positive reaction could be obtained if it was carried out in concentrated guanidine hydrochloride solution. This medium should therefore be used to prove the presence of sulfhydryl groups in treated keratin. The application of the nitroprusside reaction in both of these media showed that the treat ment with thioglycollate differed from other cases in that it produced two kinds of sulfhydryl groups. Some of the groups reacted with nitroprusside in an aqueous medium, while some did so only in guanidine hydrochloride solution. Similarly, the detection of the disulfide groups of untreated keratin by means of potassium cyanide and nitroprusside should also be brought about in concentrated guanidine hydrochloride solution, because the color does not appear in aqueous medium. At temperatures of 65° and 100°C, according to Phillips et al., the treatment of wool with aqueous solutions of potassium cyanide leads to an almost quantitative conversion of the com bined cystine into lanthionine. However, such wool also gives a strong coloration with nitro prusside in guanidine hydrochloride solution. This cannot be caused by lanthionine, and is therefore in contradiction to the assumed quantitative nature of the formation of lanthionine under the specified conditions.

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