L-Glucose
Encyclopedia
L-Glucose is an organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 with formula C6H12O6 or H–(C=O)–(CHOH)5–H, specifically one of the aldohexose
Aldohexose
An aldohexose is a hexose with an aldehyde group on one end.The aldohexoses have four chiral centres for a total of 16 possible aldohexose stereoisomers . Of these, only three commonly occur in nature: D-glucose, D-galactose, and D-mannose...

 monosaccharide
Monosaccharide
Monosaccharides are the most basic units of biologically important carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose , fructose , galactose, xylose...

s. Its molecular structure is an enantiomer
Enantiomer
In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...

 of the more common D-glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

.

L-Glucose does not occur naturally in higher living organisms, but can be synthesized
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...

 in the laboratory. L-Glucose is indistinguishable in taste from D-glucose, but cannot be used by living organisms as source of energy because it cannot be phosphorylated by hexokinase
Hexokinase
A hexokinase is an enzyme that phosphorylates a six-carbon sugar, a hexose, to a hexose phosphate. In most tissues and organisms, glucose is the most important substrate of hexokinases, and glucose-6-phosphate the most important product....

, the first enzyme in the glycolysis
Glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...

 pathway.
One of the known exceptions is in Burkholderia caryophylli
Burkholderia caryophylli
Burkholderia caryophylli is a plant pathogenic bacterium, which can cause wilt, foot and root rot on carnation....

, the enzyme D-threo-aldolse dehydrogenase is capable of oxidising L-glucose

Like the 'D-' isomer, L-glucose usually occurs as one of four cyclic tautomers — α- and β-L-glucopyranose (the most common, with a six-atom ring), and α- and β-L-glucofuranose (with a five-atom ring). In solution, these isomers interconvert in matters of hours, with the open-chain form as an intermediate stage.

Uses

L-Glucose was once proposed as a low-calorie sweetener, but was never marketed due to excessive manufacturing costs.

The L-glucose derivative, L-glucose pentaacetate, was found to stimulate insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....

 release, and might therefore be of therapeutic value for type 2 diabetes
Diabetes mellitus type 2
Diabetes mellitus type 2formerly non-insulin-dependent diabetes mellitus or adult-onset diabetesis a metabolic disorder that is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency. Diabetes is often initially managed by increasing exercise and...

. L-Glucose was also found to be a laxative
Laxative
Laxatives are foods, compounds, or drugs taken to induce bowel movements or to loosen the stool, most often taken to treat constipation. Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and/or bowel examinations, and may be supplemented by enemas under...

, and proposed as a colon-cleansing agent which would not produce the disruption of fluid and electrolyte levels associated with the significant liquid quantities of bad-tasting osmotic laxatives conventionally used in preparation for colonoscopy
Colonoscopy
Colonoscopy is the endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. It may provide a visual diagnosis and grants the opportunity for biopsy or removal of suspected...

.
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