Galactose
Galactose (Gal) (also called
brain sugar) is a type of
sugar found in
dairy products, in
sugar beets and other
gums and
mucilages. It is also
synthesized by the body, where it forms part of
glycolipids and
glycoproteins in several
tissues. It is considered a nutritive
sweetener because it has
food energy. Galactose is less sweet than glucose and not very water-soluble.
Galactan is a
polymer of the sugar galactose. It is found in
hemicellulose and can be converted to galactose by
hydrolysis.
Galactose is a
monosaccharide constituent, together with
glucose, of the
disaccharide lactose. The
hydrolysis of lactose to glucose and galactose is
catalyzed by the
enzyme beta-galactosidase, a
lactase. In the human body, glucose is changed into galactose in order to enable the
mammary glands to secrete lactose.
Two studies have suggested a possible link between galactose in milk and
ovarian cancer.[
1][
2] Other studies failed to show such a link.
The first and last -OH groups point the same way and the second and third -OH groups point the other way. D-Galactose has the same configuration at its
penultimate carbon as D-
glyceraldehyde.Galactose is an optical isomer of glucose.
Galactose and glucose are produced by hydrolysis of
lactose by
ß-galactosidase. This enzyme is produced by the
lac operon in
Escherichia coli (
E. coli).
There are 3 important disorders involving galactose:
*
Galactokinase deficiency causes
cataracts and mental retardation. If a galactose-free diet starts sufficiently early, the cataracts will regress without complications however neurological damage is permanent.
*
UDPgalactose-4-epimerase deficiency is extremely rare (only 2 reported cases). It causes
nerve deafness.
*
Galactose-1-phosphate uridyl transferase deficiency is the most problematic, as galactose-free diets do not have considerable long-term effects.
