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Galactose (, + , sometimes abbreviated Gal, is a common monosaccharide, i.e. a simple sugar. It is classified as a reducing hexose, more specifically an aldohexose. In terms of structure, it is a C-4 epimer of glucose. A white, water-soluble solid, it is about as sweetness as glucose, and about 65% as sweet as sucrose.
D-Galactose is also known as brain sugar since it is a component of (oligosaccharide-protein compounds) found in Nerve tissue tissue. Galactofuranose occurs in bacteria, fungi and protozoa, and is recognized by a putative chordate immune lectin intelectin through its exocyclic 1,2-diol.
In nature, lactose is found primarily in milk and milk products. Consequently, various food products made with dairy-derived ingredients can contain lactose. Galactose is metabolism to glucose by the three principal enzymes in a mechanism known as the Leloir pathway. The enzymes are listed in the order of the metabolic pathway: galactokinase (GALK), galactose-1-phosphate uridyltransferase (GALT), and UDP-galactose 4′-epimerase (GALE).
In human lactation, galactose is required in a 1 to 1 ratio with glucose to enable the mammary glands to synthesize and secrete lactose. In a study where women were fed a diet containing galactose, 69 ± 6% of glucose and 54 ± 4% of galactose in the lactose they produced were derived directly from Blood plasma glucose, while 7 ± 2% of the glucose and 12 ± 2% of the galactose in the lactose, were derived directly from plasma galactose. 25 ± 8% of the glucose and 35 ± 6% of the galactose was synthesized from smaller molecules in a process referred to in the paper as Gluconeogenesis. This suggests that the synthesis of galactose is supplemented by direct uptake and of use of plasma galactose when present.
Four isomers are cyclic, two of them with a pyranose (six-membered) ring and two with a furanose (five-membered) ring. Each cyclic form can exist as two , named alpha and beta, since a new stereocenter is generated upon cyclization at the site of the carbonyl. In the pyranose form, the OH group on C-3 is axial.
The main pathway of galactose metabolism is the Leloir pathway; humans and other species, however, have been noted to contain several alternate pathways, such as the De Ley Doudoroff Pathway. The Leloir pathway consists of the latter stage of a two-part process that converts β-D-galactose to UDP-glucose. The initial stage is the conversion of β-D-galactose to α-D-galactose by the enzyme, mutarotase (GALM). The Leloir pathway then carries out the conversion of α-D-galactose to UDP-glucose via three principal enzymes: Galactokinase (GALK) phosphorylates α-D-galactose to galactose-1-phosphate, or Gal-1-P; Galactose-1-phosphate uridyltransferase (GALT) transfers a UMP group from UDP-glucose to Gal-1-P to form UDP-galactose; and finally, UDP galactose-4'-epimerase (GALE) interconverts UDP-galactose and UDP-glucose, thereby completing the pathway.
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The above mechanisms for galactose metabolism are necessary because the human body cannot directly use galactose for energy metabolism, and it must first go through one of these processes. (2026). 9783827429889 ISBN 9783827429889
Galactosemia is an inability to properly break down galactose due to a genetically inherited mutation in one of the enzymes in the Leloir pathway. As a result, the consumption of even small quantities is harmful to galactosemics.
Some ongoing studies suggest 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.
Galactose is a component of the (chemical markers) present on blood cells that distinguish blood type within the ABO blood group system. In O and A antigens, there are two of galactose on the antigens, whereas in the B antigens there are three monomers of galactose. (1995). 9780697222138, WM C. Brown. ISBN 9780697222138
A disaccharide composed of two units of galactose, galactose-alpha-1,3-galactose (alpha-gal), has been recognized as a potential allergen present in mammal meat. Alpha-gal allergy may be triggered by lone star tick bites.
Galactose in sodium saccharin solution has also been found to cause conditioned flavor avoidance in adult female rats within a laboratory setting when combined with intragastric injections. The reason for this flavor avoidance is still unknown. However, a decrease in the levels of the enzymes required to convert galactose to glucose in the liver of the rats could be responsible.
Galactose was first isolated and studied by Louis Pasteur in 1856 and he called it "lactose". In 1860, Berthelot renamed it "galactose" or "glucose lactique"."Galactose" — from the Ancient Greek (gálaktos, "milk"). In 1894, Emil Fischer and Robert Morrell determined the configuration of galactose. The configuration of galactose appears on page 385.
The Proton NMR spectra for galactose includes peaks at 4.7 ppm (D2O), 4.15 ppm (−CH2OH), 3.75, 3.61, 3.48 and 3.20 ppm (−CH2 of ring), 2.79–1.90 ppm (−OH).
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