Common microenvironments of tyrosyl residues in several bence jones proteins

Abstract

A comparison was made of the reactivities toward iodination of particular tyrosyl residues in κ Bence-Jones proteins of subgroups I, II and III. They are Roy (I), Cum (II), Ti (III) and Col (III). For each of these proteins the positions of all the tyrosines in the primary structure are known. In all the proteins Tyr 173 is highly reactive and Tyr 186 is less reactive. Another interesting feature is that in all the proteins, the rate constant for incorporation of the first iodine is greater than that for incorporation of the second iodine in the case of Tyr 173 while for Tyr 186 the opposite situation was found. Thus, all four of the Bence-Jones proteins have one common microenvironment around Tyr 173 and another common environment around Tyr 186, showing that the tertiary structure of each of the proteins is the same in the region of Tyr 173 and is also the same in the region of Tyr 186. Tyr 36 in Ti and Col is of low reactivity and thus appears to be partially buried. It appears that in all κ Bence-Jones proteins the microenvironment of Tyr 173 is hydrophilic and that of Tyr 186 is hydrophobic.