Mannose
- (2S, 3S, 4R, 5R) - Pentahydroxyhexanal
- (2R, 3R, 4S, 5S) - Pentahydroxyhexanal
- D: 3458-28-4
- L: 10030-80-5
Colorless and odorless, crystalline powder
Fixed
1.54 g · cm -3
- D: 133 ° C
- L: 129-131 ° C
Readily soluble in water ( 713 g · l -1 at 17 ° C)
Template: Infobox chemical / molecular formula search available
Mannose is an epimer of glucose. As D -Mannose is a natural hexose and block numerous plant polysaccharides ( mannans ). In the body, it is mainly a component of membranes. Based on sucrose has a 10 % solution a sweetening power of 59%. L- mannose has little meaning.
Chemistry of mannose
Behavior in aqueous solution
In aqueous solution it is partly to an intramolecular ring closure, resulting in a balance between the aldehyde and the two ring forms ( furanose form and pyranose form) is established, then the mannose is present almost exclusively in the pyranose form:
Mannose synthesis
The glucose-6- glucose -6-phosphate isomerase is converted analogously to the glycolysis to fructose -6- phosphate, which in turn is isomerized by means of the mannose-6 -phosphate isomerase to mannose -6- phosphate. A further rearrangement to mannose -1-phosphate is catalyzed by the enzyme phosphomannomutase.
Degradation of mannose
Where free mannose in a cell, it is phosphorylated by the enzyme hexokinase to mannose -6- phosphate, making it lipophobic to the cell no longer be able to leave. If it is not needed to build new glycoproteins, it is converted via the mannose phosphate isomerase to fructose -6-phosphate, which in turn can be supplied from energy gain of the glycolysis.
GDP-mannose
A characteristic of the Mannose is that their activation does not uridine triphosphate ( UTP), but takes place over guanosine triphosphate (GTP ). For this purpose, mannose -6-phosphate is first converted to mannose -1 - phosphate, which then reacts further to GDP- mannose. The reaction sequence here is the same as in the reaction of glucose to UDP-glucose and glycogen synthesis.
Toxicity to insects
While mannose for humans is virtually non-toxic, has this for various Hymenoptera such as bees ( which also include the bumblebees ) and the Common Wasp Vespa vulgaris high toxicity. For bees, a lethal dose of 0.4-0.5 mg was identified. The toxic effect is due to the similarity of the mannose to glucose, which results in a competitive inhibition of various enzymes.