The structural environment of functional amino acid
residues has been determined by chemical modification and
subsequent differential peptide mapping of GI (173). It has
long been recognized that GI catalyzes the isomerization of
both glucose and xylose. However, whether the reactions occur
at the same site or at two different sites was not known. The
presence of a single active site for isomerization of both glucose
and xylose was demonstrated (68) by using a kinetic
method elaborated by Keleti et al. (95).