Allolactose

Allolactose
Names
	IUPAC name 6-O-β-D-Galactopyranosyl-D-glucopyranose
	Systematic 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
CAS Number	28447-39-4 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:36229 ;
ChemSpider	4957195 ;
PubChem CID	67375559;
UNII	C7B2C5KXF9 ;
CompTox Dashboard (EPA)	DTXSID80893952 ;
	InChI InChI=1S/C12H22O11/c13-1-3-5(14)8(17)10(19)12(23-3)21-2-4-6(15)7(16)9(18)11(20)22-4/h3-20H,1-2H2/t3-,4-,5+,6-,7+,8+,9-,10-,11?,12-/m1/s1 Key: DLRVVLDZNNYCBX-VDGMBKLFSA-N ; InChI=1/C12H22O11/c13-1-3-5(14)8(17)10(19)12(23-3)21-2-4-6(15)7(16)9(18)11(20)22-4/h3-20H,1-2H2/t3-,4-,5+,6-,7+,8+,9-,10-,11?,12-/m1/s1 Key: DLRVVLDZNNYCBX-VDGMBKLFBT;
	SMILES O[C@H]1[C@H](O)[C@H](OC(O)[C@@H]1O)CO[C@@H]2O[C@H](CO)[C@H](O)[C@H](O)[C@H]2O;
Properties
Chemical formula	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). verify (what is ?) Infobox references

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.

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.

Mechanism of Allolactose Formation:

β-Galactosidase (lacZ) plays a dual role in the lac operon system. Not only does it break down lactose into glucose and galactose, but it also catalyzes the transformation of lactose into allolactose, the molecule that induces the lac operon. The enzyme facilitates this conversion via a glucose-binding site, which temporarily holds glucose after cleavage from lactose. Despite the enzyme’s relatively low affinity for glucose, the exact details of this glucose-binding site have remained difficult to pinpoint. Research using a modified version of β-galactosidase (G794A) has provided structural insights, confirming that the glucose in the trapped allolactose molecule binds to a specific site on the enzyme.^[1]

External links

allolactose at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
Illustration of function

^ Wheatley, Robert W.; Lo, Summie; Jancewicz, Larisa J.; Dugdale, Megan L.; Huber, Reuben E. (2013-05). "Structural Explanation for Allolactose (lac Operon Inducer) Synthesis by lacZ β-Galactosidase and the Evolutionary Relationship between Allolactose Synthesis and the lac Repressor". Journal of Biological Chemistry. 288 (18): 12993–13005. doi:10.1074/jbc.M113.455436. PMC 3642343. PMID 23486479. {{cite journal}}: Check date values in: |date= (help)CS1 maint: unflagged free DOI (link)

[1] Wheatley, Robert W.; Lo, Summie; Jancewicz, Larisa J.; Dugdale, Megan L.; Huber, Reuben E. (2013-05). "Structural Explanation for Allolactose (lac Operon Inducer) Synthesis by lacZ β-Galactosidase and the Evolutionary Relationship between Allolactose Synthesis and the lac Repressor". Journal of Biological Chemistry. 288 (18): 12993–13005. doi:10.1074/jbc.M113.455436. PMC 3642343. PMID 23486479. {{cite journal}}: Check date values in: |date= (help)CS1 maint: unflagged free DOI (link)

[1]

See also

External links