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Enzyme Nomenclature
Information on EC 2.4.1.22 - lactose synthase
Word Map on EC 2.4.1.22
- 2.4.1.22
-
milk
-
beta-lactoglobulin
-
mammary
- gland
-
whey
- lysozyme
- casein
-
globule
-
molten
- calcium
- epithelial
- glycoprotein
- oligosaccharide
- prolactin
-
beta-casein
-
refolding
-
galactosylation
- lactoferrin
- n-acetylglucosamine
- goat
-
explants
-
dairy
-
alpha-casein
-
beta-lg
-
n-glycans
- glycosyltransferases
-
ca2+-binding
-
lactogen
-
kappa-caseins
-
native-like
-
ovalbumin
-
cheese
-
udder
-
fucosylated
- macropus
-
breast-fed
-
alpha-crystallin
-
apomyoglobin
- lactoperoxidase
- colostral
-
skim
-
intramammary
-
mid-pregnant
- wallaby
- n-acetyllactosamine
- allergy
-
egg-white
-
beta-domain
-
holstein
-
virgin
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The expected taxonomic range for this enzyme is: Eukaryota, Bacteria
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EC NUMBER 
COMMENTARY 
2.4.1.22
-
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RECOMMENDED NAME
GeneOntology No.
lactose synthase
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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
BRENDA Link
KEGG Link
MetaCyc Link
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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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ORGANISM
COMMENTARY
LITERATURE
UNIPROT
SEQUENCE DB
SOURCE
long isoform of alpha-lactalbumin; South African fur seal
UniProt
short isoform of alpha-lactalbumin; South African fur seal
UniProt
long isoform of alpha-lactalbumin; subantarctic fur seal
UniProt
short isoform of alpha-lactalbumin; subantarctic fur seal
UniProt
-
-
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catalytic domain of recombinant bovine beta4Gal-T1 from residues 130 to 402, d129 beta4Gal-T1, 33000 Da, and mouse recombinant alpha-lactalbumin
-
-
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GENERAL INFORMATION
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
malfunction
malfunction
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sequence variations of bovine alpha-lactalbumin are associated with differences in milk yield
malfunction
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sequence variations of bovine alpha-lactalbumin are associated with differences in milk yield
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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
-
inversion of anomeric configuration to form beta-O-galactosides
-
-
?
alpha-UDP-D-galactose + N-acetyl-D-glucosamine
UDP + alpha-D-galactosyl(1-4)beta-N-acetyl-D-glucosamine
-
-
-
-
?
UDP-D-galactose + D-glucose
UDP + lactose
-
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
-
-
?
UDP-glucose + N-acetyl-D-glucosamine
UDP + D-glucosyl(1-4)beta-N-acetyl-D-glucosamine
-
about 20% activity compared to UDP-galactose
-
-
?
dUDPgalactose + D-glucose
lactose + dUDP
-
dUDPgalactose is 80% as effective as UDP-D-galactose
-
-
?
UDP-galactose + D-glucose
UDP + lactose
-
-
-
?
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 + 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
-
-
-
-
?
UDP-galactose + N-acetyl-D-glucosamine
UDP + D-galactosyl(1-4)beta-N-acetyl-D-glucosamine
-
-
-
-
?
UDP-galactose + N-acetyl-D-glucosamine
UDP + D-galactosyl(1-4)beta-N-acetyl-D-glucosamine
-
-
-
-
?
UDPgalactose + D-glucose
lactose + UDP
-
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
-
-
?
additional information
?
-
-
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
-
-
-
additional information
?
-
-
molecular interaction with different donor substrates, overview, the enzyme undergoes transition from open to close conformation upon binding of donor or acceptor substrate, overview
-
-
-
additional information
?
-
-
c-LacdiNAcS is auto-lacdiNAcylated and can synthesize GalNAc(beta1-4)GlcNAc structures on cellular glycoproteins
-
-
-
additional information
?
-
-
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
-
-
-
additional information
?
-
-
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
-
-
-
additional information
?
-
-
acceptor substrate specificity, no activity with D-galactose, N-acetylgalactosamine, glucosamine, and lactose as acceptor substrates, overview
-
-
-
additional information
?
-
-
beta1,4-galactosyltransferase-I forms a complex with alpha-lactalbumin to give lactose synthase
-
-
-
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NATURAL SUBSTRATES
NATURAL PRODUCTS
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
A7TWS3, A7TWS4
-
-
-
?
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METALS and IONS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
Mn2+
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INHIBITORS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
alpha-lactalbumin
-
inhibits galactosyl transfer to N-acetylglucosamine
-
carbodiimide
-
at pH 4.5 rapid loss of the biological activity of alpha-lactalbumin
Dimethyl-(2-hydroxy-5-nitrobenzyl)-sulfonium bromide
-
modification of alpha-lactalbumin
dithiothreitol
-
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
-
at pH 4.5 rapid loss of the biological activity of alpha-lactalbumin
additional information
-
alpha-lactalbumin strongly inhibits the transfer of galactose to free N-acetylglucosamine
-
iodoacetate
-
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
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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
additional information
additional information
-
steady-state kinetics for random and ordered bi bi mechanism, overview
-
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TURNOVER NUMBER [1/s]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
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SPECIFIC ACTIVITY [µmol/min/mg]
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
additional information
additional information
-
development of a high-throughput mass spectrometry multisubstrate assay method
additional information
-
beta1,4-galactosyltransferase in in milk of cows from several breeds at various stages of lactation, overview
additional information
-
development of a simple and fast pH-sensitive assay method using phenol red as pH-indicator, activities at different temperatures, overview
additional information
-
development of a simple and fast pH-sensitive assay method using phenol red as pH-indicator, overview
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pH OPTIMUM
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
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TEMPERATURE OPTIMUM
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
30
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TEMPERATURE RANGE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
20 - 37
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SOURCE TISSUE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
SOURCE
-
concentrations of lactose synthase components alpha-lactalbumin and beta1,4-galactosyltransferase in milk of cows from several breeds at various stages of lactation, overview
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LOCALIZATION
ORGANISM
UNIPROT
COMMENTARY
GeneOntology No.
LITERATURE
SOURCE
-
alpha-lactalbumin in synthesized on the rough endoplasmic reticulum
-
alpha-lactalbumin is a soluble milk protein secreted throughout lactation
-
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PDB
SCOP
CATH
ORGANISM
UNIPROT
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MOLECULAR WEIGHT
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
14500
-
1 * 14500, alpha-lactalbumin, + 1 * 46000, galactosyl transferase, equilibrium sedimentation
46000
-
1 * 14500, alpha-lactalbumin, + 1 * 46000, galactosyl transferase, equilibrium sedimentation
60000
-
complex between galactosyl transferase and alpha-lactalbumin, equilibrium sedimentation
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SUBUNITS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
dimer
-
1 * 14500, alpha-lactalbumin, + 1 * 46000, galactosyl transferase, equilibrium sedimentation
additional information
additional information
-
MW of lactalbumin determined by nucleotide sequence MW of lactalbumin determined by nucleotide sequence: 14179 Da; the three main polypeptides determined by SDS-PAGE of galactosyl transferase are active: 54000 Da, 48000 Da and 42000 Da
additional information
-
MW of lactalbumin determined by nucleotide sequence: guinea pig
additional information
-
MW of lactalbumin determined by nucleotide sequence MW of lactalbumin determined by nucleotide sequence: 14071 Da
additional information
-
galactosyl transferase component has a MW of 49000 Da, SDS-PAGE
additional information
-
the enzyme is composed of two structurally and functionally dissimilar proteins: 1. UDP-galactose:N-acetylglucosamine-beta4-galactosyl transferase, EC 2.4.1.90. Its normal function is to catalyze the incorporation of galactose into 1,4-linkage with N-acetylglucosamine during the synthesis of oliogosaccharide prosthetic groups of certain glycoproteins, free N-acetylglucosamine also serves as an excellent acceptor for galactose leading to the formation of N-acetylgalactosamine, 2. alpha-lactalbumin, interaction of alpha-lactalbumin with the transferase leads to lactose synthesis when UDP-galactose and glucose are present
additional information
-
the enzyme is 1.1 complex of a catalytic component beta1,4-galactosyltransferase (beta4gal-T1) and a regulatory component, alpha-lactalbumin
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POSTTRANSLATIONAL MODIFICATION
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
glycoprotein
glycoprotein
-
isolation of minor amounts of alpha-lactalbumin in milk which contains carbohydrate prosthetic group. Galactosyl transferase contains a considerable proportion of oligosaccharides
glycoprotein
-
the glycoprotein contains 1.1% sialic acid, 5.03% galactosamine, 2.47% glucosamine, 2.36% galactose, 0.87% mannose and 0.87% fucose
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Crystallization/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
catalytic domain of recombinant bovine beta4Gal-T1 from residues 130 to 402, d129 beta4Gal-T1, 33000 Da, and mouse recombinant alpha-lactalbumin. Crystal structure of enzyme bound with various substrates
-
wild-type and mutant enzyme in closed conformation induced by UDP-galactose, X-ray diffraction structure determination and analysis at 2.3 A resolution, re-refinement or previously determined crystal structures of enzyme complexed with different substrates and Mn2+, overview
-
catalytic domain of recombinant bovine beta4Gal-T1 from residues 130 to 402, d129 beta4Gal-T1, 33000 Da, and mouse recombinant alpha-lactalbumin. Crystal structure of enzyme bound with various substrates
-
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Purification/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
galactosyl transferase component
recombinant enzyme fro Escherichia coli
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Cloned/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, aberrant splicing is responsible for the two cDNA variants isolated from mammary tissue, with the longer variant maintaining the third intron and the shorter variant, phylogenetic analysis; DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, aberrant splicing is responsible for the two cDNA variants isolated from mammary tissue, with the longer variant maintaining the third intron and the shorter variant, phylogenetic analysis
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, phylogenetic analysis
expression in Escherichia coli
gene B4GALT1, DNA and amino acid sequence determination and analysis, RT-PCR expression analysis, sequence comparison
-
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, aberrant splicing is responsible for the two cDNA variants isolated from mammary tissue, with the longer variant maintaining the third intron and the shorter variant, phylogenetic analysis; DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, aberrant splicing is responsible for the two cDNA variants isolated from mammary tissue, with the longer variant maintaining the third intron and the shorter variant, phylogenetic analysis
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, aberrant splicing is responsible for the two cDNA variants isolated from mammary tissue, with the longer variant maintaining the third intron and the shorter variant, phylogenetic analysis; DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, aberrant splicing is responsible for the two cDNA variants isolated from mammary tissue, with the longer variant maintaining the third intron and the shorter variant, phylogenetic analysis
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, phylogenetic analysis
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, phylogenetic analysis
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, phylogenetic analysis
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, phylogenetic analysis
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, phylogenetic analysis
DNA and amino acid sequence determination and analysis of alpha-lactalbumin component of the lactose synthase complex, phylogenetic analysis
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ENGINEERING
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
C342T
-
determination and analysis of the closed conformation crystal structure of enzyme mutant in complex with UDP-galactose
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LINKS TO OTHER DATABASES (specific for EC-Number 2.4.1.22)
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