The Iodination of Wool

When wool is iodinated with aqueous solutions of iodine in potassium iodide at different pH values and temperatures, reaction with the tyrosine side‐chains is incomplete, even under the most favourable conditions. With alcoholic solutions of iodine, however, 96% of the tyrosine is converted into 3:5‐di‐iodotyrosine in 72 hr. at 22‐2d̀c., and there is no combination with either histidine or tryptophan. The fact that tyrosine can be iodinated exclusively and almost completely by such a simple procedure affords a useful means of discovering whether the lysine and tyrosine side‐chains are cross‐linked when wool is treated with formaldehyde. Since the amount of iodine which combines with the formaldehyde‐treated wool, after loosely held formaldehyde has been removed with phosphoric acid, is the same as for untreated wool, it is concluded that the lysine and tyrosine side‐chains are not cross‐linked by formaldehyde. It has been shown also that the distribution of tyrosine along the length of single fibres can be determined by taking radiophotographs after the fibres have been iodinated with 131 I.