(Gal) (also called brain sugar
) is a type of sugar
which is less sweet
. 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
It is also synthesized by the body, where it forms part of glycolipids and glycoproteins in several tissues.
Relationship to lactose
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).
Two 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 isomerism
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
Galactose is a epimer
Liver galactose metabolism
In 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
There are 3 important disorders involving galactose: