Galactose
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224536653
2008-07-09T08:39:44Z
159.149.161.238
{{Chembox new
| ImageFileL1 = Beta-D-Galactopyranose.svg
| ImageSizeL1 =
| ImageFileR1 = DL-Galactose num.svg
| ImageSizeR1 = 150 px
| IUPACName =
| OtherNames =
| Section1 = {{Chembox Identifiers
| CASNo = 26566-61-0
| PubChem = 6036
| SMILES =
| MeSHName = Galactose
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>
| MolarMass = 180.08
| Appearance =
| Density =
| MeltingPt = 167 degrees C
| BoilingPt =
| Solubility =
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| Section3 = {{Chembox Hazards
| MainHazards =
| FlashPt =
| Autoignition =
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}}
'''Galactose''' (Gal) (also called '''brain sugar'''<ref>''Compact American Medical Dictionary.'' Houghton Mifflin Reference Books (1998). ISBN 0395884098</ref>) 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.
==Sources==
It is found in [[dairy product]]s, in [[sugar beet]]s and other [[natural gum|gum]]s and [[mucilage]]s.
It is also [[Biosynthesis|synthesized]] by the body, where it forms part of [[glycolipid]]s and [[glycoprotein]]s in several [[Biological tissue|tissue]]s.
==Relationship to lactose==
Galactose is a [[monosaccharide]] constituent, together with [[glucose]], of the [[disaccharide]] [[lactose]]. The [[hydrolysis]] of lactose to glucose and galactose is [[catalysis|catalyzed]] by the [[enzyme]] [[lactase]], a [[beta-galactosidase|β-galactosidase]]. In the human body, glucose is changed into galactose in order to enable the [[mammary gland]]s to secrete lactose.
Galactose and glucose are produced by [[hydrolysis]] of [[lactose]] by [[lactase|β-galactosidase]]. This enzyme is produced by the [[Lac operon|''lac'' operon]] in [[Escherichia coli|''Escherichia coli'']] (''E. coli'').
==Clinical significance==
Two studies have suggested a possible link between galactose in milk and [[ovarian cancer]].<ref>{{cite journal |author=Cramer D |title=Lactase persistence and milk consumption as determinants of ovarian cancer risk |journal=Am J Epidemiol |volume=130 |issue=5 |pages=904–10 |year=1989 |pmid=2510499}}</ref><ref>{{cite journal |author=Cramer D, Harlow B, Willett W, Welch W, Bell D, Scully R, Ng W, Knapp R |title=Galactose consumption and metabolism in relation to the risk of ovarian cancer |journal=Lancet |volume=2 |issue=8654 |pages=66–71 |year=1989 |pmid=2567871 |doi=10.1016/S0140-6736(89)90313-9}}</ref> Other studies show no correlation, even in the presence of defective galactose metabolism.<ref>{{cite journal |author= Marc T. Goodman , Anna H. Wu , Ko-Hui Tung , Katharine McDuffie , Daniel W. Cramer , Lynne R. Wilkens , Keith Terada , Juergen K. V. Reichardt , and Won G. Ng |title=Association of Galactose-1-Phosphate Uridyltransferase Activity and N314D Genotype with the Risk of Ovarian Cancer |journal=Am. J. Epidemiol |volume=156 |issue=8 |pages=693–701 |year=2002 |pmid=12370157 |doi=10.1093/aje/kwf104}}</ref><ref>{{cite journal |author=Fung, W. L. Alan, Risch, Harvey, McLaughlin, John, Rosen, Barry, Cole, David, Vesprini, Danny, Narod, Steven A. |title=The N314D Polymorphism of Galactose-1-Phosphate Uridyl Transferase Does Not Modify the Risk of Ovarian Cancer |journal= Cancer Epidemiol Biomarkers Prev |volume=12 |issue=7 |pages=678–80 |year=2003 |pmid=12869412}}</ref> 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.<ref>{{cite journal|author=Genkinger, Jeanine M., Hunter, David J., Spiegelman, Donna, Anderson, Kristin E., Arslan, Alan, Beeson, W. Lawrence, Buring, Julie E., Fraser, Gary E., Freudenheim, Jo L., Goldbohm, R. Alexandra, Hankinson, Susan E., Jacobs, David R., Jr., Koushik, Anita, Lacey, James V., Jr., Larsson, Susanna C., Leitzmann, Michael, McCullough, Marji L., Miller, Anthony B., Rodriguez, Carmen, Rohan, Thomas E., Schouten, Leo J., Shore, Roy, Smit, Ellen, Wolk, Alicja, Zhang, Shumin M., Smith-Warner, Stephanie A. |title=Dairy Products and Ovarian Cancer: A Pooled Analysis of 12 Cohort Studies|journal=Cancer Epidemiol Biomarkers Prev |volume=15 |pages=364–372 |year=2006 |pmid=16492930 | doi = 10.1158/1055-9965.EPI-05-0484 <!--Retrieved from CrossRef by DOI bot-->}}</ref> 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).{{Fact|date=February 2007}} This effect is likely to be a result of binding of galactose to FSGS factor.{{Fact|date=February 2007}}
==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 [[beta carbon|penultimate carbon]] as D-[[glyceraldehyde]].
Galactose is a [[epimer]] of [[glucose]].
==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
^ \
/ v
UDP-glc UDP-gal
^ /
\___________/
epimerase
==Metabolic disorders==
There are 3 important disorders involving galactose:
{| class="wikitable"
| '''Name''' || '''Enzyme''' || '''Description'''
|-
| ''[[Galactosemia]]'' || [[Galactokinase]] || Causes [[cataract]]s 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]] || Is the most problematic, as galactose-free diets do not have considerable long-term effects.
|}
==References==
<references/>
{{Carbohydrates}}
[[Category:Monosaccharides]]
[[Category:Aldohexoses]]
[[Category:Nutrition]]
[[Category:Sweeteners]]
[[ar:جالكتوز]]
[[ca:Galactosa]]
[[cs:Galaktosa]]
[[da:Galaktose]]
[[de:Galactose]]
[[es:Galactosa]]
[[fr:Galactose]]
[[gl:Galactosa]]
[[it:Galattosio]]
[[he:גלקטוז]]
[[la:Galactosium]]
[[hu:Galaktóz]]
[[ms:Galaktosa]]
[[nl:Galactose]]
[[ja:ガラクトース]]
[[no:Galaktose]]
[[oc:Galactòsa]]
[[pl:Galaktoza]]
[[pt:Galactose]]
[[ru:Галактоза]]
[[sr:Галактоза]]
[[sh:Galaktoza]]
[[fi:Galaktoosi]]
[[sv:Galaktos]]
[[th:กาแล็กโทส]]
[[tr:Galaktoz]]
[[zh:半乳糖]]