To complete the isomerization, Glu357 donates its proton to C1, the C2 hydroxyl group loses its proton and the open-chain ketose fructose 6-phosphate is formed.
22.
Rough mechanism showing cis-enediol intermediateMPI must convert an aldose ( mannose ) to a ketose ( fructose ), in addition to opening and closing the rings for these sugars.
23.
Otherwise, the molecule has a keto group, a carbonyl " ( C = O ) " between two carbons; then it is formally a ketone, and is termed a ketose.
24.
In carbohydrate chemistry, the Lobry de Bruyn van Ekenstein transformation is the base or acid-catalyzed transformation of an aldose into the ketose isomer or vice versa, with a tautomeric enediol as reaction intermediate.
25.
It will give a positive result for aldose monosaccharides ( due to the oxidisable aldehyde group ) but also for ketose monosaccharides, as they are converted to aldoses by the base in the reagent, and then give a positive result.
26.
Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone, and gives a positive test because it is converted to the aldoses glucose and mannose by the base in the reagent.
27.
These hydroxyl groups at C-3 and C-4 of the ketose donor must be in the D-" threo " configuration in order to correctly correspond to the C-1 and C-2 positions on the aldose acceptor.
28.
Other instances are Aldose-ketose isomerism in biochemistry; isomerizations between conformational isomers, which take place without an actual rearrangement for instance inconversion of two cyclohexane conformations; fluxional molecules which display rapid interconversion of isomers e . g . bullvalene; and " valence isomerization " : the isomerization of molecules which involve structural changes resulting only from a relocation of single and double bonds.
