Kynurenine Located within Keratin Proteins Isolated from Photoyellowed Wool Fabric

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Abstract
This paper describes the identification of the yellow chromophore-containing residue kynurenine within photoyellowed wool. Photoyellowed Merino wool fabric was tryptically digested and the resultant peptides were separated by high-performance liquid chromatography. Peaks with absorbance at 400 nm were collected and analyzed by tandem quadrupole time-of-flight mass spec-trometry. Kynurenine was identified as a yellow chromophore in two peptide sequences characteristic of Type 1 intermediate filament and high glycine-tyrosine wool proteins. To our knowledge this is the first conclusive evidence confirming the identity of photoyellowed products and their location within the primary structure of wool proteins. A number of non-yellow modifications were identified in the course of this study and taken together with the identification of kynurenine modifications, these results support the current mechanistic theory of the radical oxidative process occurring during photoyellowing.