Photochemical Degradation of Keratins

Abstract

Twenty-nine samples of fur, hair. wool and feathers have been irradiated with a Sunlamp (A max. 310 nm) and with a 2 kW mercury vapour lamp emitting mixed U.V. and visible radiation resembling sunlight. Photodegradation is accompanied by progressive yellowing when irradiated with the Sunlamp. It is accompanied by bleaching followed by yellowing, or by bleaching throughout irradiation if the initial yellowness is high, when exposed to the 2 kW lamp. A group of nine fur and hair samples, representing four different orders of mammals, are the most sensitive to yellowing, followed by a group of ten wool and hair samples from the Artiodactyla and finally by the feather keratins which are less susceptible than the a-keratins. Amino acid analysis of the keratins before and after Sunlamp irradiation shows strong correlation of yellowing both with the initial concentration of tryptophan and with its destruction during irradiation. Similar correlations of yellowing with destruction of other amino acids are less significant. Preliminary washing with non-ionic detergent increases susceptibility to U.V. yellowing.

Loss of tryptophan associated with photopolymerization and yellowing of proteins exposed to light over 300nm

“…The marked difference in the colour between the S-carboxymethylated lysozyme and ribonuclease supports the observations of Lennox & Rowlands (1969) that photo-oxidative breakdown products of tryptophan are the major cause of photo-oxidative yellowing.…”

Photo-Oxidation Mechanisms in Wool. A Study of the Photoprotective Effect of a Thiourea/Formaldehyde Treatment

“…Lennox and Rowlands [18] have shown, using 29 different types of keratin, that there is a correlation between the tryptophyl content of keratin and its susceptibility to uv yellowing. By analyzing the photo-induced changes in the amino acid composition of natural and fluorescent-whitened wool and silk, Leaver and Ramsay [15J were able to demonstrate that the rate of yellowing parallels very closely the rate of photo-oxidation of the tryptophyl side-chains.…”

Sensitized Photo‐oxidation of Wool and Silk by a Triazinylstilbene

“…The present situation as regards the loss of amino acids on irradiation of untreated wool keratin has been summarized [8]; tryptophyl residues are thought to be the most susceptible to photo-oxidation, although cystyl, tyrosyl, methionyl and histidyl residues are also partially destroyed. These amino acids are also susceptible to dye-sensitized photo-oxidation, and have been studied extensively [11][12][13][14][15][16].…”