galactose

Galactose (Gal) (also called brain sugar) is a type of sugar which is less sweet than glucose. It is considered a nutritive sweetener because it has food energy.

Galactan is a polymer of the sugar galactose. It is found in hemicellulose and can be converted to galactose by hydrolysis. Galactose solubility in water is 68.30 grams per 100 grams of water at 20–25° C.

It is 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.

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 lactase, a β-galactosidase. In the human body, glucose is changed into galactose in order to enable the mammary glands to secrete lactose.

Galactose and glucose are produced by hydrolysis of lactose by β-galactosidase. This enzyme is produced by the lac operon in Escherichia coli (E. coli).

In the liver, galactose is converted to glucose 6-phosphate.

Pathology

 Galactosemia Galactokinase

• 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

• UDPgalactose-4-epimerase Is extremely rare (only 2 reported cases). It causes nerve deafness.

 Galactose-1-phosphate uridyl transferase deficiency

• Galactose-1-phosphate uridyl transferase

References

 Petry KG, Reichardt JK. The fundamental importance of human galactose metabolism: lessons from genetics and biochemistry. Trends Genet. 1998 Mar;14(3):98-102. PMID: 9540406