Allolactose

Allolactose is a disaccharide similar to lactose. It consists of the monosaccharides D-galactose and D-glucose linked through a β1-6 glycosidic linkage instead of the β1-4 linkage of lactose. It may arise from the occasional transglycosylation of lactose by β-galactosidase.

Allolactose
Names
IUPAC name
(3R,4S,5S,6R)-6-[[(2R,3R,4S,5R,6R)-3,4,5-Trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxymethyl]oxane-2,3,4,5-tetrol
Other names
6-O-β-D-Galactopyranosyl-D-glucose; β-D-Galactopyranosyl (1→6)-D-glucose
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
Properties
C12H22O11
Molar mass 342.296 g/mol
Density 1.768 g/mL
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

It is an inducer of the lac operon in Escherichia coli and many other enteric bacteria. It binds to a subunit of the tetrameric lac repressor, which results in conformational changes and reduces the binding affinity of the lac repressor to the lac operator, thereby dissociating it from the lac operator. The absence of the repressor allows the transcription of the lac operon to proceed. A non-hydrolyzable analog of allolactose, isopropyl β-D-1-thiogalactopyranoside (IPTG), is normally used in molecular biology to induce the lac operon.

See also
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