States of Tyrosyl and Tryptophyl Residues in Bence Jones Proteins<xref ref-type="fn" rid="fn1"><sup>*</sup></xref>

Abstract

The states of tyrosyl and tryptophyl residues in six preparations of type K and type L Bence Jones proteins were investigated by means of chemical modification and ultraviolet absorption spectroscopy. Modifications of the tyrosyl and tryptophyl residues were performed with N-acetylimidazole (NAI)*** and 2-hydroxyl-5-nitrobenzy[ bromide (HNB bromide),*** respectively. Two type K proteins and two out of four type L proteins had a tyrosyl residue per molecular weight of 22, 500 which is acetylated at low concentrations of NAI. At higher concentrations of NAI, additional two tyrosy] residues were acetylated. Other two type L proteins were exceptional; one had three and the other had five NAI-reactive tyrosyl residues. In the native state, no tryptophyl residue in a type K protein (Ta) was modified with HNB bromide. A type L protein (Fu) had one HNB-bromide-reactive tryptophyl residue. In 6 M urea, all the tryptophyl residues (two for Ta protein and three for Fu protein) were modified. Difference absorption spectra showed that one of two buried tryptophyl residues of these proteins was exposed upon acid denaturation and the other was exposed on further treatment of the acid-denatured proteins with 6 M urea. It was suggested that the tryptophyl residue which is located on the surface of the Fu protein molecule is Trp-187.