An aldose is a monosaccharide with a carbon backbone chain with a carbonyl group on the endmost carbon atom, making it an aldehyde, and hydroxyl groups connected to all the other carbon atoms. Aldoses can be distinguished from ketoses, which have the carbonyl group away from the end of the molecule, and are therefore ketones.
Isomerases are a general class of enzymes that convert a molecule from one isomer to another. Isomerases facilitate intramolecular rearrangements in which bonds are broken and formed. The general form of such a reaction is as follows:
A heptose is a monosaccharide with seven carbon atoms.
Glucose-6-phosphate isomerase (GPI), alternatively known as phosphoglucose isomerase/phosphoglucoisomerase (PGI) or phosphohexose isomerase (PHI), is an enzyme that in humans is encoded by the GPI gene on chromosome 19. This gene encodes a member of the glucose phosphate isomerase protein family. The encoded protein has been identified as a moonlighting protein based on its ability to perform mechanistically distinct functions. In the cytoplasm, the gene product functions as a glycolytic enzyme that interconverts glucose-6-phosphate (G6P) and fructose-6-phosphate (F6P). Extracellularly, the encoded protein functions as a neurotrophic factor that promotes survival of skeletal motor neurons and sensory neurons, and as a lymphokine that induces immunoglobulin secretion. The encoded protein is also referred to as autocrine motility factor (AMF) based on an additional function as a tumor-secreted cytokine and angiogenic factor. Defects in this gene are the cause of nonspherocytic hemolytic anemia, and a severe enzyme deficiency can be associated with hydrops fetalis, immediate neonatal death and neurological impairment. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Jan 2014]
The Kiliani–Fischer synthesis, named for German chemists Heinrich Kiliani and Emil Fischer, is a method for synthesizing monosaccharides. It proceeds via synthesis and hydrolysis of a cyanohydrin, followed by reduction of the intermediate acid to the aldehyde, thus elongating the carbon chain of an aldose by one carbon atom while preserving stereochemistry on all the previously present chiral carbons. The new chiral carbon is produced with both stereochemistries, so the product of a Kiliani–Fischer synthesis is a mixture of two diastereomeric sugars, called epimers. For example, D-arabinose is converted to a mixture of D-glucose and D-mannose.
In carbohydrate chemistry, the Lobry de Bruyn–Van Ekenstein transformation also known as the Lobry de Bruyn–Alberda 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. Ketoses may be transformed into 3-ketoses, etcetera. The enediol is also an intermediate for the epimerization of an aldose or ketose.
Mannose-6 phosphate isomerase (MPI), alternately phosphomannose isomerase (PMI) is an enzyme which facilitates the interconversion of fructose 6-phosphate (F6P) and mannose-6-phosphate (M6P). Mannose-6-phosphate isomerase may also enable the synthesis of GDP-mannose in eukaryotic organisms. M6P can be converted to F6P by mannose-6-phosphate isomerase and subsequently utilized in several metabolic pathways including glycolysis and capsular polysaccharide biosynthesis. PMI is monomeric and metallodependent on zinc as a cofactor ligand. PMI is inhibited by erythrose 4-phosphate, mannitol 1-phosphate, and to a lesser extent, the alpha anomer of M6P.
In enzymology, a 4-deoxy-L-threo-5-hexosulose-uronate ketol-isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, an arabinose-5-phosphate isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, an arabinose isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a D-lyxose ketol-isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a galactose-6-phosphate isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a glucuronate isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a hydroxypyruvate isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a L-arabinose isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a L-fucose isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a L-rhamnose isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a ribose isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a S-methyl-5-thioribose-1-phosphate isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a xylose isomerase is an enzyme that catalyzes the interconversion of D-xylose and D-xylulose. This enzyme belongs to the family of isomerases, specifically those intramolecular oxidoreductases interconverting aldoses and ketoses. The isomerase has now been observed in nearly a hundred species of bacteria. Xylose-isomerases are also commonly called fructose-isomerases due to their ability to interconvert glucose and fructose. The systematic name of this enzyme class is D-xylose aldose-ketose-isomerase. Other names in common use include D-xylose isomerase, D-xylose ketoisomerase, and D-xylose ketol-isomerase.
