Relative Reactivity to Iodination of Tyrosine Residues in α-Chymotrypsin

The relative reactivity toward iodination of each of the 4 tyrosine residues in chymotrypsin was determined. The results showed that the reactivities of the tyrosine residues in native uniodinated chymotrypsin are in the order 146 g 94 g 171 g 229 with relative reactivities of 1:0.4 and 0.2:0.02, respectively. The relative reactivities indicate that one of the C chain tyrosines, namely 229, is buried since it is at most only 10% as reactive as the next least reactive tyrosine.