The presence of an aspartate
or glutamate residue in GI was documented by its
inactivation by Woodward’s reagent K or guanidine hydrochloride
(74, 172). Involvement of carboxylate residues is implicated
in the binding of metal ion cofactors (34). Chemical
modification of protected and unprotected GI and subsequent
peptide mapping allowed the identification of an active-site
region with a consensus sequence consisting of Phe-His-Xaa-
Asp-Xaa-Xaa-Pro-Xaa-Gly (173). The results of studies on the
chemical modification of GI complement the conclusions
drawn on the basis of X-ray crystallographic studies.