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Fischer projection of D-glyceraldehyde. Like most carbohydrates, simple aldoses have the general chemical formula C n (H 2 O) n.Because formaldehyde (n=1) and glycolaldehyde (n=2) are not generally considered to be carbohydrates, [1] the simplest possible aldose is the triose glyceraldehyde, which only contains three carbon atoms.
In enzymology, aldose reductase (or aldehyde reductase) (EC 1.1.1.21) is an enzyme in humans encoded by the gene AKR1B1.It is an cytosolic NADPH-dependent oxidoreductase that catalyzes the reduction of a variety of aldehydes and carbonyls, including monosaccharides, and primarily known for catalyzing the reduction of glucose to sorbitol, the first step in polyol pathway of glucose metabolism.
Aldose reductase activity increases as the glucose concentration rises in diabetes in those tissues that are not insulin sensitive, which include the lenses, peripheral nerves, and glomerulus. Sorbitol does not diffuse through cell membranes easily and therefore accumulates, causing osmotic damage which leads to retinopathy and neuropathy .
In enzymology, an aldose 1-dehydrogenase (EC 1.1.1.121) is an enzyme that catalyzes the chemical reaction D-aldose + NAD + ⇌ {\displaystyle \rightleftharpoons } D-aldonolactone + NADH + H + Thus, the two substrates of this enzyme are D-aldose and NAD + , whereas its 3 products are D-aldonolactone , NADH , and H + .
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The polyol metabolic pathway. [6]Cells use glucose for energy.This normally occurs by phosphorylation from the enzyme hexokinase. However, if large amounts of glucose are present (as in diabetes mellitus), hexokinase becomes saturated and the excess glucose enters the polyol pathway when aldose reductase reduces it to sorbitol.
In enzymology, an aldose 1-epimerase (EC 5.1.3.3) is an enzyme that catalyzes the chemical reaction alpha-D-glucose ⇌ {\displaystyle \rightleftharpoons } beta-D-glucose Hence, this enzyme has one substrate , alpha-D-glucose , and one product , beta-D-glucose .
Aldonic acids are the products of the oxidation of aldoses by Benedict's or Fehling's reagents. [7] Copper ions react with an aldose to form a red precipitate, Cu 2 O. The reaction scheme of an aldose being oxidized by the copper ions in a Benedict's reagent solution. The R group provided is an example of a sugar backbone.