A NINHYDRIN HISTOCHEMICAL TEST SPECIFIC FOR HAIR KERATIN

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Abstract
The reaction of ninhvdrin with α-amino groups of amino acids and proteins results in deamination of the amino acid or protein to form a nitrogen-containing blue dye complex. This molecule is small and highly diffusible, a property which was utilized in the development of a ninhvdrin histochemical test specific for hair keratin. Using a silicone rubber cement. which is resistant to boiling solutions, for the attachment of tissue sections to slides, the sections could be boiled in a ninhydrin solution. The ninhydrin reaction product is lost to the surrounding medium in the case of all tissues except hair keratin. Hair keratin is stained blue. No other keratin. including epidermal keratin or inner root sheath keratin. stains by this method. Although the exact chemistry of the reaction is unknown. evidence is cited for the probability that only a certain molecular arrangement of cystine in a polypeptide chain found almost exclusively in hair keratin can form an attachment site for the dye molecules.