Carbohydrates exist in a variety of isomeric forms, they have stereoisomers, molecules that have the same molecular formula but differ in their spatial arrangement. Carbohydrates can have a D-configuration or L-configuration, known as enantiomers, these are mirror images of each other. The D/L configuration is dictated by the asymmetrical carbon in the carbohydrate carbon chain which is furthest from the aldehyde or ketone group. Most of the carbohydrates found in vertebrates are in the D-configuration. An example is the hexose carbohydrate, D-glucose, the carbon5 (C5) is the furthermost asymmetrical carbon from the aldehyde group, CH2OH group on the C5 lies in the equatorial plane and the Hydrogen is in the axial plane. In its enantiomer L-glucose this configuration is reversed, the Hydrogen in the equatorial plane and the CH2OH group in the axial.
- ↑ Berg JM, Tymoczko JL, Gatto GJ, Stryer L: Biochemistry. 8th Ed, New York: W.H. Freeman and Company. 2015: p317