LacY is selective for disaccharides containing a Dgalactopyranosyl
ring as well as D-galactose (12–14) but does not
interact with D-glucopyranosides or D-glucose (14–16). The
specificity of LacY is clearly directed toward the galactopyranosyl
ring of substrate, and galactose is the most specific substrate
but has very low affinity (14). Although the C4 OH group is by
far the most important for specificity, the C2, C3, and C6 OH
groups are also important for binding (C4 OH C3 OH C6
OH C2 OH) (14, 16).