Galactan is a polymer of the sugar galactose. It is present 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.
Structure and isomerism:
Galactose exists in both open-chain and cyclic form. The open-chain form has a carbonyl at the end of the chain.Four isomers are cyclic and two of them with a pyranose (six-membered) ring, two with a furanose (five-membered) ring. Galactofuranose occurs in bacteria, fungi and protozoa.
Galactose and lactose:
Galactose is a monosaccharide. When combined with glucose, thro a dehydration reaction, the result is the disaccharide lactose. The hydrolysis of lactose to form glucose and galactose is catalyzed by the enzyme lactase, a ß-galactosidase.
In the human body, glucose is converted into galactose via hexoneogenesis in order to enable the mammary glands to secrete lactose. However, most galactose in breast milk is synthesizes from galactose taken up from the blood, and only 35?6% is made by de novo synthesis. Glycerol also helps some to the mammary galactose production.
Galactose and glucose are made by hydrolysis of lactose by ß-galactosidase. This enzyme is made by the lac operon in Escherichia coli.
Sources:
It is found in dairy products, sugar beets, gums and mucilages.
It can be produced from the body, where it forms part of glycolipids and glycoproteins in several tissues.
Clinical significance:
Chronic system exposure of mice, rats, and Drosophila to D-galactose causes the acceleration of senescence and has been used as an aging model. More recently, pooled analysis made 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.
Galactose
Galactose is in the same family as sucrose, fructose and lactose.
Galactose is found in milk and whey, as well as the human body.
Nursing infants obtain the galactose required for their development and maturation from mother's milk.
Galactose contributes directly (as well as through bonds by way of contact points on cells) to vital information and control processes in the body. It also functions as a fundamental and structural substance for cells, cell walls, and intracellular matrix.
Galactose is obtained from a protein-free distillate of whey and lactose.
High doses of galactose have a laxative effect; it is otherwise absolutely harmless.
Galactose is produced in two- to ten-gram quantities (per day) by all healthy people. This D(+) galactose has a simple sugar structure and is a basic building block of life.
Galactose is a simple sugar, without a doubt. However, it is also of considerable importance to the human organism, more than one would expect of a "simple" sugar. The following example serves to illustrate this:
The human blood types impressively illustrate the biological importance of carbohydrates in glycolipids. The following diagram depicts the terminal sugars or monosaccharides (simple sugars) of the main blood types O, A and B.
Blood types A and B only differ from blood type O by the presence of an additional monosaccharide, N-acetylgalactosamine for type A and galactose for type B. Expressed another way, blood types O and B differ only by one galactose molecule. This apparently small difference makes the difference between life and death for the human organism in blood transfusions.
This illustrative role of galactose in the human body is completely independent of the oral consumption of galactose. It is merely demonstrative of the curious juxtaposition of the simplicity of the substance and its importance to the body. It is similar to a brick. In itself it is a rather "boring" item; in the imagination of an architect and with skilled hands it can become a work of art.
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