Lactose (galactose and glucose disaccharide) à Galactose à Galactose-1-Phosphate à Glucose-1-phosphate

Galactose is converted into Galactose-1-phosphate by Galactokinase (which if deficient may result in mild Galactosemia).

Galactose-1-phosphate is converted to Glucose-1-phosphate by Galactose-1-phosphate uridyltransferase (which if deificient will result in severe galactosemia: mental retardation, cataracts, hepatosplenomegaly).

Lactose (glucose + galactose) à 1 Glucose + 1 galactose     [lactase]

1 Galactose à Galactose-1-phosphate   [galactokinase]

Galactose-1-phosphate à Glucose-1-phosphate [galactose-1-phosphate uridyltransferase]

Glucose-1-phosphate à Glucose-6-phosphate [phosphoglucomutase]