Action of Ninhydrin on Keratin

Abstract

ALTHOUGH ninhydrin has long been used as a sensitive reagent for the detection of amino-acids, its remarkable cross-linking action on protein fibres appears to be unknown. In the case of wool keratin, the reaction, the extent of which is independent of pH between pH 4.8 and 8.3, takes place slowly at ordinary temperatures and is incomplete in 48 hr. With a boiling 0.0685 M solution at pH 4.8, however, cross-linking proceeds so rapidly that after treatment for 15 min. the fibres show a 25.8 per cent increase in resistance to extension (30 per cent) in water at 22.2° C. Since the extent of reaction is reduced when the lysine side-chains are blocked by means of 1-fluoro-2 : 4-dinitrobenzene or nitroso-benzene, and since no strengthening is obtained with completely deaminated fibres, the basic side-chains of keratin must play a fundamental part in the cross-linking reaction.