Abstract
It is believed that yellowing of silk fibers by light is based upon the photochemical changes of tyrosine groups in fibroin.
The authors prepared tyrosine polymer and confirming this point, applied it on the white rayon clothes and then irradiated them with Atlas fade-O-meter. The yellowing of the clothes was hardly recognized. Same colour reactions such as Neubauer-Rhode's, Nessler's or xanthoprotein reactions were tested on the treated clothes. The states of colouring were very different from the case of silk fabrics. Adding a small quantity of tryptophan on them, however, the states of yellowing and other reactions became similar to those of the silk fabrics. These results show that the yellowing of proteinous fibers is not due to the changes of tyrosine but those of tryptophan.
It was also recognized that tyrosine residues of the polymer were promptly decomposed by light. The authors tried to identify the decomposed products and got some unknown substances coloured by Pauli's diazo reagent, but neither amino, imino acids, indole compounds nor other expected substances were identified.
