Galactose
- D-( ) -galactose
- L-(- ) -galactose
- (2R, 3S, 4S, 5R) - Pentahydroxyhexanal
- (2S, 3R, 4R, 5S) - Pentahydroxyhexanal
- D- Form: 59-23-4
- L- shape: 15572-79-9
White solid
Fixed
1.5 g · cm -3 ( D- shape )
- D / L ( α - form): 163-165 ° C
- D- isomer ( β - form): 143-145 ° C
- Well in hot water
- Poorly in ethanol and diethyl ether
Template: Infobox chemical / molecular formula search available
The galactose ( LSP case), short- Gal, and galactose (traditional spelling by gr γαλακτόζη galaktóze from του γάλακτος tou Galaktos " from milk " ) or the mucus sugar, is a naturally occurring chemical compound from the group of monosaccharides ( simple sugars ). Galactose occurs, for example in most living organisms as a building block of oligo-and condensation polymers of carbohydrates in various mucous membranes before whence is derived the German name. Based on sucrose has a 10% D- galactose a sweetening power of 63%. Galactose, as do most natural sugars D-configuration.
Properties
Galactose is a hexose, and like all hexoses the molecular formula C6H12O6. It is stereoisomer ( more specifically, a C4 - epimer ) for glucose and is part of the subset of aldohexoses.
Behavior in aqueous solution
In aqueous solution it is partly to an intramolecular ring closure so that an equilibrium is established between the Aldoform and the two ring forms ( furanose form and pyranose form):
At 20 ° C is dissolved in water before D -galactose to 32 % in the α - pyranose form, to 64 % in the β - pyranose form, to 1% in the α - furanose and 3% in the β - furanose form.
Specific rotation values
- α -D - galactopyranose ( = six-membered ring ): [ α ] 20 D = 150.7 °
- β -D - galactopyranose [ α ] 20 ° / D = 52.8 °
Galactose shows mutarotation. Rotation of the aqueous solution: [ α ] 20 ° / D = 80.2 °
Occurrence
Galactose occurs in addition to the monosaccharides form also as a building block in di-, oligo -and polysaccharides ( lactose, raffinose ) and other biochemical substances on.
As a part of the mother's milk is an important energy source for infants. Galactose is absorbed in the small intestine and metabolized in the liver either by the enzyme α -galactosidase, or incorporated by uridine diphosphate glucose into glycogen (see " energy metabolism ").
Disease
An inherited disorder in which the affected galactose can not use due to an enzyme defect, galactosemia is called. It comes immediately after birth to fruition.
Energy metabolism
Thus, the galactose can be used for energy, it must be introduced into one of the usual metabolic pathways - in this case in glycolysis. The degradation of the galactose is as follows:
- With the help of galactokinase (GK, EC 2.7.1.6 ), galactose ( 1) is phosphorylated to galactose -1 -phosphate ( 2) consumption of ATP.
- In the next step, the enzyme galactose -1-phosphate uridyl transferase (GALT, EC 2.7.7.12 ) is the involvement of UDP -glucose, (3) at the reactant: The result of UDP-galactose (4 ), and glucose -1-phosphate (5 ). This enzyme is defective in a galactosemia.
- The enzyme phosphoglucomutase (PGM, EC 5.4.2.2 ), can be isomerized glucose-1- phosphate to glucose -6-phosphate (6), an intermediate of glycolysis. In addition, from glucose -1-phosphate with UTP ( uridine triphosphate ) by the UDP-glucose pyrophosphorylase ( EC 2.7.7.9 ) are regenerated into UDP -glucose.
- The enzyme UDP-glucose 4-epimerase ( UGE, EC 5.1.3.2 ) ensures that from UDP- galactose to UDP-glucose can be regenerated. It can be used again for the reaction in the second step or the glycogen biosynthesis.