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Information on EC 2.4.1.22 - lactose synthase
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2.4.1.22 lactose synthaseIUBMB Comments
The enzyme is a complex of two proteins, A and B. In the absence of the B protein (alpha-lactalbumin), the enzyme catalyses the transfer of galactose from UDP-alpha-D-galactose to N-acetylglucosamine (EC 2.4.1.90 N-acetyllactosamine synthase).
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Word Map
- 2.4.1.22
- milk
- beta-lactoglobulin
- whey
- casein
- lysozyme
-
globule
-
molten
- beta-casein
- oligosaccharide
- lactoferrin
- prolactin
- goat
- n-acetylglucosamine
- infant
-
dairy
- immunoglobulin
- n-glycans
-
galactosylation
-
sialylated
- kappa-caseins
- ovalbumin
- alpha-casein
- bsa
-
beta-lg
-
native-like
- allergy
- glycosyltransferases
-
ca2+-binding
-
refolding
-
complex-type
- lactoperoxidase
- wallaby
-
intramammary
- macropus
-
beta-domain
-
udder
- apomyoglobin
-
cheese
-
breast-fed
-
virgin
-
globule-like
- n-acetyllactosamine
-
formula-fed
- alpha-crystallin
-
skim
-
fucosylated
-
egg-white
-
lactogen
- colostrum
- glycoconjugates
The expected taxonomic range for this enzyme is: Eukaryota, Bacteria
Synonyms
alpha-lactalbumin, b4galt1, beta-1,4-galactosyltransferase, lacdinac, lactose synthase, lactose synthetase, beta1,4-galactosyltransferase, lalba, beta4gal-t1, ugt72b1, 
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SYNONYM 
ORGANISM
UNIPROT
COMMENTARY 
LITERATURE
alpha-lactalbumin
B4GALT1
beta-1,4-galactosyltransferase
beta1,4-galactosyltransferase
c-LacdiNAcS
-
exhibits N-acetylgalactosaminyltransferase activity in the absence of exogenous alpha-lactalbumin as well as other glycosyltransferase activities including lactose synthase, and beta1,4-galactosyltransferase 1
Gal-T1
glactosyltransferase, uridine diphosphogalactose-glucose
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-
-
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lactose synthase
lactose synthetase
LALBA
N-acetyllactosamine synthase
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-
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UDP-galactose-glucose galactosyltransferase
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-
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UDPgalactose-glucose galactosyltransferase
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-
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additional information
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the lactose synthase complex is composed of alpha-lactalbumin and beta1,4-galactosyltransferase components
lactose synthetase
-
-
-
-
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REACTION
REACTION DIAGRAM
COMMENTARY
ORGANISM
UNIPROT
LITERATURE
UDP-alpha-D-galactose + D-glucose = UDP + lactose
-
-
-
-
UDP-alpha-D-galactose + D-glucose = UDP + lactose
random or ordered bi bi mechanism
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REACTION TYPE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
hexosyl group transfer
-
-
-
-
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PATHWAY SOURCE
PATHWAYS
KEGG
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SYSTEMATIC NAME
IUBMB Comments
UDP-galactose:D-glucose 4-beta-D-galactosyltransferase
The enzyme is a complex of two proteins, A and B. In the absence of the B protein (alpha-lactalbumin), the enzyme catalyses the transfer of galactose from UDP-alpha-D-galactose to N-acetylglucosamine (EC 2.4.1.90 N-acetyllactosamine synthase).
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CAS REGISTRY NUMBER
COMMENTARY
9030-11-9
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SUBSTRATE
PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate)
(Substrate)
LITERATURE
(Substrate)
(Substrate)
COMMENTARY
(Product)
(Product)
LITERATURE
(Product)
(Product)
Reversibility
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
alpha-UDP-D-galactose + D-glucose
UDP + lactose
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inversion of anomeric configuration to form beta-O-galactosides
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-
?
alpha-UDP-D-galactose + N-acetyl-D-glucosamine
UDP + alpha-D-galactosyl(1-4)beta-N-acetyl-D-glucosamine
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-
-
-
?
UDP-alpha-D-galactose + O-beta-D-xylosyl-[IgG antibody]
UDP + 4-beta-D-galactosyl-O-beta-D-xylosyl-[IgG antibody]
antibody (Lo-BM2) expressed in Nicotiana tabacum strain BY-2 cells
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-
?
UDP-D-galactose + D-glucose
UDP + lactose
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lactose synthesis is achieved only in the presence of alpha-lactalbumin. In absence of alpha-lactalbumin the enzyme catalyzes the reaction of EC 2.4.1.90
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-
?
UDP-glucose + N-acetyl-D-glucosamine
UDP + D-glucosyl(1-4)beta-N-acetyl-D-glucosamine
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about 20% activity compared to UDP-galactose
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-
?
dUDPgalactose + D-glucose
lactose + dUDP
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dUDPgalactose is 80% as effective as UDP-D-galactose
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-
?
UDP-galactose + D-glucose
UDP + lactose
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-
-
?
UDP-galactose + D-glucose
UDP + lactose
residues necessary for lactose synthesis activity are Phe31, His32, Leu110, Gln117 and Trp118 of alpha-lactalbumin
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-
?
UDP-galactose + D-glucose
UDP + lactose
residues necessary for lactose synthesis activity are Phe31, His32, Leu110, Gln117 and Trp118 of alpha-lactalbumin
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-
?
UDP-galactose + D-glucose
UDP + lactose
residues necessary for lactose synthesis activity are Phe31, His32, Leu110, Gln117 and Trp118 of alpha-lactalbumin
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-
?
UDP-galactose + D-glucose
UDP + lactose
residues necessary for lactose synthesis activity are Phe31, His32, Leu110, Gln117 and Trp118 of alpha-lactalbumin
-
-
?
UDP-galactose + D-glucose
UDP + lactose
residues necessary for lactose synthesis activity are Phe31, His32, Leu110, Gln117 and Trp118 of alpha-lactalbumin
-
-
?
UDP-galactose + D-glucose
UDP + lactose
residues necessary for lactose synthesis activity are Phe31, His32, Leu110, Gln117 and Trp118 of alpha-lactalbumin
-
-
?
UDP-galactose + D-glucose
UDP + lactose
residues necessary for lactose synthesis activity are Phe31, His32, Leu110, Gln117 and Trp118 of alpha-lactalbumin
-
-
?
UDP-galactose + D-glucose
UDP + lactose
residues necessary for lactose synthesis activity are Phe31, His32, Leu110, Gln117 and Trp118 of alpha-lactalbumin
-
-
?
UDP-galactose + N-acetyl-D-glucosamine
UDP + D-galactosyl(1-4)beta-N-acetyl-D-glucosamine
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-
-
?
UDP-galactose + N-acetyl-D-glucosamine
UDP + D-galactosyl(1-4)beta-N-acetyl-D-glucosamine
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?
UDP-galactose + N-acetyl-D-glucosamine
UDP + D-galactosyl(1-4)beta-N-acetyl-D-glucosamine
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?
UDPgalactose + D-glucose
lactose + UDP
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the galactosyl transferase can catalyze the transfer of galactose to glucose to form lactose in the absence of alpha-lactalbumin provided the glucose concentration is high
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?
additional information
?
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upon substrate binding to beta4Gal-T1, a large conformational change occurs in the region comprising residues 345 to 365. The role of alpha-lactalbumin is to hold glucose by hydrogen bonding with the O-1 hydroxyl group in the acceptor-binding site on beta4Gal-T1, while the N-acetyl group-binding pocket in beta4Gal-T1 adjusts to maximize the interactions with the glucose molecule
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?
additional information
?
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molecular interaction with different donor substrates, overview, the enzyme undergoes transition from open to close conformation upon binding of donor or acceptor substrate, overview
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?
additional information
?
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c-LacdiNAcS is auto-lacdiNAcylated and can synthesize GalNAc(beta1-4)GlcNAc structures on cellular glycoproteins
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?
additional information
?
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acceptor substrate specificity, no activity with D-galactose, N-acetylgalactosamine, glucosamine, and lactose as acceptor substrates, no activity with UDP-glucose as donor substrate, overview
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?
additional information
?
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the enzyme interacts with UDP-galactose transporter SLC35A2
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additional information
?
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upon substrate binding to beta4Gal-T1, a large conformational change occurs in the region comprising residues 345 to 365. The role of alpha-lactalbumin is to hold glucose by hydrogen bonding with the O-1 hydroxyl group in the acceptor-binding site on beta4Gal-T1, while the N-acetyl group-binding pocket in beta4Gal-T1 adjusts to maximize the interactions with the glucose molecule
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-
?
additional information
?
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acceptor substrate specificity, no activity with D-galactose, N-acetylgalactosamine, glucosamine, and lactose as acceptor substrates, overview
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-
?
additional information
?
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beta1,4-galactosyltransferase-I forms a complex with alpha-lactalbumin to give lactose synthase
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-
?
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NATURAL SUBSTRATE
NATURAL PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate)
(Substrate)
LITERATURE
(Substrate)
(Substrate)
COMMENTARY
(Product)
(Product)
LITERATURE
(Product)
(Product)
REVERSIBILITY
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
UDP-galactose + D-glucose
UDP + lactose
-
-
-
?
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METALS and IONS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
Mn2+
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INHIBITOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
alpha-lactalbumin
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inhibits galactosyl transfer to N-acetylglucosamine
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carbodiimide
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at pH 4.5 rapid loss of the biological activity of alpha-lactalbumin
Dimethyl-(2-hydroxy-5-nitrobenzyl)-sulfonium bromide
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modification of alpha-lactalbumin
dithiothreitol
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the rate of reduction of the disulfide bond in alpha-lactalbumin is much faster with dithiothreitol than mercaptoethanol, and at 24°C proceeds to completion within minutes at pH 8
glycinamide
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at pH 4.5 rapid loss of the biological activity of alpha-lactalbumin
iodoacetate
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modification of alpha-lactalbumin, carboxymethylation proceeds in the order His68, His32, His107. The activity decreases progressively as carboxymethylation proceeds, the fully carboxymethylated derivative has about 40% of the activity of the unmodified alpha-lactalbumin in lactose synthetase assay
additional information
-
alpha-lactalbumin strongly inhibits the transfer of galactose to free N-acetylglucosamine
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ACTIVATING COMPOUND
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
alpha-lactalbumin
-
enhances equally the binding of N-acetylglucosamine or glucose to the galactosyl transferase
-
alpha-lactalbumin
-
alters the acceptor specificity of the galactosyltransferase and thereby increases lactose synthesis and decreases N-acetylglucosamine synthesis
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KM VALUE [mM]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE