MECHANISM OF ACTION
Despite its commercial importance, very little information is
available about the structural and mechanistic properties of
GI. The catalytic mechanism of GI has been a subject of great
interest to researchers. Earlier, GI was assumed to function in
a manner similar to sugar phosphate isomerases and to follow
the ene-diol mechanism (136) (Fig. 2a). Recent studies have
attributed the action of GI to a hydride shift mechanism (Fig.
2c). Knowledge of active-site configuration is a prerequisite for
studying the structure-function relationship of the enzyme.
Different approaches have been used to study the active site of
GI and to delineate its mechanism of action. These include (i)
chemical modification, (ii) X-ray crystallography, and (iii) isotope
exchange. The main features of the mechanism proposed
for GI are ring opening of the substrate, isomerization via a
hydride shift from C-2 to C-1, and ring closure of the product.