The galactose and glucose have similar structures; that is, they are epimerase. Several reactions are required for this sugar to enter the glycolytic pathway. Galactose is initially converted to galactose-1-phosphate by galactokinase.

The galactose-1-phosphate is transformed into the nucleotide derivative UDP galactose. During fetal development and childhood, the first step in this conversion is catalysed by galactose-1-phosphate by uridyltransferase. Beginning in adolescence, UDP-galactose is produced in a reaction caralysed by UDP-galactose pyrophosphorylase as shown in Figure 8.32.

Figure 8.32 Metabolism of Galactose

Then UDP -glucose is formed by the isomerisation of galactose catalysed by UDPglucose-4-epimerase. Depending on the cell’s metabolic needs, UDP-glucose is used directly in glycogen synthesis or is converted to glucose-1-phosphate by UDP-glucose pyrophosphorylase. Glucose-1-phosphate enters the glycolytic pathway after its conversion to glucose-6-phosphate by phosphoglucomutase.