galactose n : a simple sugar found in lactose [syn: brain sugar]
- Catalan: galactosa
- Danish: galaktose
- French: galactose
- Italian: galattosio
- Spanish: galactosa
Galactose (Gal) (also called brain sugar) is a type of sugar which is less sweet than glucose and not very water-soluble. 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.
It is also synthesized by the body, where it forms part of glycolipids and glycoproteins in several tissues.
Relationship to lactoseGalactose 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).
Clinical significanceTwo studies have suggested a possible link between galactose in milk and ovarian cancer. Other studies show no correlation, even in the presence of defective galactose metabolism. More recently, pooled analysis done by the Harvard School of Public Health showed no specific correlation between lactose containing foods and ovarian cancer, and showed statistically insignificant increases in risk for consumption of lactose at ≥30 g/d. More research is necessary to ascertain possible risks.
There are some ongoing studies which suggest that galactose may have a role in treatment of focal segmental glomerulosclerosis (a kidney disease resulting in kidney failure and proteinuria). This effect is likely to be a result of binding of galactose to FSGS factor.
Structure and isomerismThe 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 a epimer of glucose.
Liver galactose metabolismIn the liver, galactose is converted to glucose 6-phosphate in the following reactions:
galacto- uridyl phosphogluco- kinase transferase mutase gal --------> gal 1 P ------------------> glc 1 P -----------> glc 6 P ^ \ / v UDP-glc UDP-gal ^ / \___________/ epimerase
Metabolic disordersThere are 3 important disorders involving galactose:
galactose in Arabic: جالكتوز
galactose in Catalan: Galactosa
galactose in Czech: Galaktosa
galactose in Danish: Galaktose
galactose in German: Galactose
galactose in Spanish: Galactosa
galactose in French: Galactose
galactose in Galician: Galactosa
galactose in Italian: Galattosio
galactose in Hebrew: גלקטוז
galactose in Latin: Galactosium
galactose in Hungarian: Galaktóz
galactose in Malay (macrolanguage): Galaktosa
galactose in Dutch: Galactose
galactose in Japanese: ガラクトース
galactose in Norwegian: Galaktose
galactose in Occitan (post 1500): Galactòsa
galactose in Polish: Galaktoza
galactose in Portuguese: Galactose
galactose in Russian: Галактоза
galactose in Serbian: Галактоза
galactose in Serbo-Croatian: Galaktoza
galactose in Finnish: Galaktoosi
galactose in Swedish: Galaktos
galactose in Thai: กาแล็กโทส
galactose in Turkish: Galaktoz
galactose in Chinese: 半乳糖