Conversion of galactose to glucose 1-phosphate. The
conversion proceeds through a sugar-nucleotide derivative, UDPgalactose,
which is formed when galactose 1-phosphate displaces glucose
1-phosphate from UDP-glucose. UDP-galactose is then converted
by UDP-glucose 4-epimerase to UDP-glucose, in a reaction that involves
oxidation of C-4 (pink) by NAD, then reduction of C-4 by
NADH; the result is inversion of the configuration at C-4. The UDPglucose
is recycled through another round of the same reaction. The
net effect of this cycle is the conversion of galactose 1-phosphate to
glucose 1-phosphate; there is no net production or consumption of
UDP-galactose or UDP-glucose.