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Allolactose
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{{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 477317994 | ImageFile = Allolactose.png | ImageSize = 200px | ImageAlt = Skeletal formula of allolactose | ImageFile1 = Allolactose-3D-balls.png | ImageAlt1 = Ball-and-stick model of the allolactose molecule | IUPACName = 6-''O''-β-<small>D</small>-Galactopyranosyl-<small>D</small>-glucopyranose |SystematicName=(3''R'',4''S'',5''S'',6''R'')-6-<nowiki>[[</nowiki>(2''R'',3''R'',4''S'',5''R'',6''R'')-3,4,5-Trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxymethyl]oxane-2,3,4,5-tetrol | OtherNames = 6-''O''-β-<small>D</small>-Galactopyranosyl-<small>D</small>-glucose; β-<small>D</small>-Galactopyranosyl (1→6)-<small>D</small>-glucose |Section1={{Chembox Identifiers | PubChem = 67375559 | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 36229 | 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 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 4957195 | InChI1 = 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 | InChIKey1 = DLRVVLDZNNYCBX-VDGMBKLFBT | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 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 | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = DLRVVLDZNNYCBX-VDGMBKLFSA-N | CASNo_Ref = {{cascite|changed|??}} | CASNo = 28447-39-4 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = C7B2C5KXF9 }} |Section2={{Chembox Properties | Formula = C<sub>12</sub>H<sub>22</sub>O<sub>11</sub> | MolarMass= 342.296 g/mol | Appearance = | Density= 1.768 g/mL | MeltingPt= | BoilingPt= | Solubility = }} |Section4={{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} }} '''Allolactose''' is a [[disaccharide]] similar to [[lactose]]. It consists of the [[monosaccharide]]s <small>D</small>-[[galactose]] and <small>D</small>-[[glucose]] linked through a β1-6 [[Glycosidic bond|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|''lac'' operon]] in ''[[Escherichia coli]]'' and many other [[Gut flora|enteric bacteria]]. It binds to a subunit of the tetrameric [[lac repressor|''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.<ref>{{Cite journal |last1=Wheatley |first1=Robert W. |last2=Lo |first2=Summie |last3=Jancewicz |first3=Larisa J. |last4=Dugdale |first4=Megan L. |last5=Huber |first5=Reuben E. |date=May 2013 |title=Structural Explanation for Allolactose (lac Operon Inducer) Synthesis by lacZ β-Galactosidase and the Evolutionary Relationship between Allolactose Synthesis and the lac Repressor |journal=Journal of Biological Chemistry |language=en |volume=288 |issue=18 |pages=12993–13005 |doi=10.1074/jbc.M113.455436 |doi-access=free |pmc=3642343 |pmid=23486479}}</ref> '''Incorporating Allolactose in Research:''' Recent studies, such as the work by Toba, Watanabe, and Adachi (1982), have demonstrated the presence of non-lactose disaccharides, including allolactose (6-O-β-D-galactopyranosyl-D-glucose) and 6-O-β-D-galactopyranosyl-D-galactose, in commercially available yogurt. These disaccharides, alongside lactose and galactose, were identified through sophisticated gas-liquid chromatography (GLC) and mass spectrometry. The research highlighted that while lactose and galactose were found in higher concentrations (ranging from 2.11% to 3.13% and 1.11% to 1.52%, respectively), allolactose and 6-O-β-D-galactopyranosyl-D-galactose were present in much smaller quantities (0.03% to 0.09%). The ability to isolate these disaccharides from yogurt using methods like dialysis and chromatography has opened new insights into the sugar composition of yogurt, beyond the more commonly studied lactose and galactose.<ref>{{Cite journal |last=Toba |first=Takahiro |last2=Watanabe |first2=Akira |last3=Adachi |first3=Susumu |date=May 1982 |title=Allolactose and 6-0-β-D-Galactopyranosyl-D-Galactose in Commercial Yogurt |url=https://doi.org/10.3168/jds.s0022-0302(82)82257-1 |journal=Journal of Dairy Science |volume=65 |issue=5 |pages=702–706 |doi=10.3168/jds.s0022-0302(82)82257-1 |issn=0022-0302}}</ref>
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