Ketohexosa

Ketohexosa, or ketohexose in English, refers to a monosaccharide with six carbon atoms and a ketone functional group. In the linear form, the carbonyl is at carbon 2, classifying the molecule as a ketose. Like other hexoses, ketohexoses have stereoisomers, including enantiomeric D- and L- forms. The most well-known member is D-fructose, a natural sweetener found in many fruits and in honey.

Other ketohexoses include sorbose, psicose (also known as allulose in some contexts), and tagatose. These sugars share the same molecular formula, C6H12O6, but differ in the arrangement of hydroxyl groups around the carbon skeleton. They occur in nature in small amounts and can be produced or interconverted by enzymes in plants and microorganisms.

Biosynthesis and metabolism: in plants, ketohexoses can arise from the isomerization of glucose derivatives. In humans, fructose is phosphorylated by ketohexokinase (fructokinase) to fructose-1-phosphate, which is then cleaved further in the liver. This pathway bypasses a key glycolytic control step and has implications for energy metabolism and lipogenesis at high intake.

Physical properties and forms: ketohexoses are highly soluble and typically sweet. In solution, they can cyclize to form furanose or, less commonly, pyranose rings, giving rise to different anomeric forms.

See also: monosaccharide, hexose, fructose.