B4GALT1

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005794 Golgi apparatus	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetically inferred Golgi residence for the GT7 family. This is the correct core compartment: B4GALT1 is a trans-Golgi resident type II membrane enzyme (codistributes with thiamine pyrophosphatase in trans-Golgi cisternae, PMID:6121819; IDA Golgi PMID:7744867). is_active_in is appropriate. Accept as a core location (the more granular Golgi membrane / Golgi trans cisterna terms are also present and preferred for specificity).
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetically inferred core catalytic activity, concordant with extensive direct experimental evidence (PMID:16157350 crystal structures + kinetics; multiple EXP/IDA annotations). This is the central, evolutionarily conserved molecular function of B4GALT1. Accept as core.
GO:0006487 protein N-linked glycosylation	IBA GO_REF:0000033	ACCEPT	Summary: Core biological process: B4GALT1 performs the galactosylation step of complex N-glycan maturation, adding Gal to terminal GlcNAc of N-glycan antennae (directly assayed in PMID:16157350; IgG Fc N-glycan galactosylation PMID:27872474). Accept as a core process.
GO:0000139 Golgi membrane	IEA GO_REF:0000117	ACCEPT	Summary: Electronic (ARBA) Golgi membrane location, consistent with the experimentally established trans-Golgi membrane residence of this type II membrane enzyme. Correct and specific; accept as core location.
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	IEA GO_REF:0000120	ACCEPT	Summary: Electronic assignment (RHEA:22932 / EC 2.4.1.38) of the core catalytic activity, redundant with the experimentally supported IBA/IDA/EXP annotations to the same term. Correct; accept.
GO:0003945 N-acetyllactosamine synthase activity	IEA GO_REF:0000120	ACCEPT	Summary: Electronic assignment (RHEA:17745 / EC 2.4.1.90) of the activity transferring Gal to free GlcNAc to make LacNAc. Experimentally supported (IDA PMID:16157350, PMID:33805, PMID:2120039) and a genuine facet of the core activity. Accept.
GO:0004461 lactose synthase activity	IEA GO_REF:0000120	ACCEPT	Summary: Electronic assignment (RHEA:12404 / EC 2.4.1.22) of the lactose synthase activity that B4GALT1 acquires in complex with alpha-lactalbumin. Experimentally supported (EXP PMID:11419947, PMID:806951; IDA PMID:33805) and a core, evolutionarily selected bifunctional activity. Accept.
GO:0005576 extracellular region	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: The UniProt secretion mapping is consistent with the processed soluble enzyme and human body-fluid biochemistry. Retain this extracellular location as non-core without assigning every extracellular detection to one molecular form.
GO:0005886 plasma membrane	IEA GO_REF:0000120	KEEP AS NON CORE	Summary: Plasma-membrane localization is consistent with the documented cell-surface pool. Relative long-form targeting does not exclude Golgi localization of that product or establish a surface-specific catalytic function.
GO:0005975 carbohydrate metabolic process	IEA GO_REF:0000002	MODIFY	Summary: Refine the InterPro-derived carbohydrate-metabolism assertion to oligosaccharide biosynthesis (GO:0009312), a descendant in the checked GO hierarchy. B4GALT1 directly assembles the disaccharides N-acetyllactosamine and, with alpha-lactalbumin, lactose. Independent human enzyme assays support these reactions. Protein N-linked glycosylation is also a core process but is not a subclass refinement of this particular term. The replacement is already represented by another source assertion and introduces no NEW annotation. Proposed replacements: oligosaccharide biosynthetic process
GO:0009986 cell surface	IEA GO_REF:0000120	KEEP AS NON CORE	Summary: Retain the documented cell-surface pool as a contextual, non-core location. Both alternative-initiation products can reach the Golgi, and this GOA row does not identify an exclusive isoform function.
GO:0016757 glycosyltransferase activity	IEA GO_REF:0000002	MODIFY	Summary: Broad InterPro grandparent term. The specific beta-1,4-galactosyltransferase activity (GO:0003831) is experimentally established and should supersede this generic term. Proposed replacements: beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity
GO:0030175 filopodium	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: UniProt explicitly transfers long-isoform filopodial localization from mouse P15535. A CC annotation does not assert a dedicated filopodial function. Retain contextual localization with its orthology limit; no direct human filopodium experiment claimed.
GO:0032580 Golgi cisterna membrane	IEA GO_REF:0000044	ACCEPT	Summary: Electronic Golgi cisterna membrane location, consistent with the trans-Golgi cisternal residence demonstrated by immuno-EM (PMID:6121819). Correct and specific; accept as a core location.
GO:0005794 Golgi apparatus	IEA GO_REF:0000107	ACCEPT	Summary: Ensembl-Compara orthology-based Golgi apparatus location, redundant with the IBA/IDA Golgi annotations. Correct core compartment. Accept.
GO:0008378 galactosyltransferase activity	IEA GO_REF:0000107	MODIFY	Summary: Parent term (galactosyltransferase activity) inferred by orthology. The specific beta-1,4-galactosyltransferase activity is experimentally established; modify to the specific child. Proposed replacements: beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity
GO:0032991 protein-containing complex	IEA GO_REF:0000107	MODIFY	Summary: The transferred complex-membership assertion is biologically sound but can be refined to catalytic complex. B4GALT1 forms the lactose-synthesizing complex with LALBA, and human GalT constructs also show Golgi-localized homo- and heteromeric associations. This refinement preserves the original orthology evidence; it does not assert one universal oligomeric state or a new lactose-specific ontology identifier. Proposed replacements: catalytic complex
GO:0005989 lactose biosynthetic process	TAS Reactome:R-HSA-5653890	ACCEPT	Summary: Reactome traceable annotation for lactose synthesis. B4GALT1, in the lactose synthase complex, is the catalytic component producing lactose in lactating mammary gland (PMID:11419947; PMID:806951). This is a genuine, tissue-specific core process. Accept.
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	TAS Reactome:R-HSA-3656230	ACCEPT	Summary: Reactome reaction ("Defective B4GALT1 does not transfer Gal to the keratan chain") annotating the core galactosyltransferase activity (here in the keratan sulfate context). Correct core MF. Accept.
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	TAS Reactome:R-HSA-4793956	ACCEPT	Summary: Reactome reaction ("Defective B4GALT1 does not add Gal to N-glycan") annotating the core N-glycan galactosyltransferase activity. Correct core MF. Accept.
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	TAS Reactome:R-HSA-9035949	ACCEPT	Summary: Reactome reaction annotating the core galactosyltransferase activity (N-glycan precursor context). Redundant with the other MF annotations; correct. Accept.
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	TAS Reactome:R-HSA-9035950	ACCEPT	Summary: Reactome reaction annotating the core galactosyltransferase activity (keratan branch context). Correct core MF. Accept.
GO:0004461 lactose synthase activity	EXP PMID:11419947 Crystal structure of lactose synthase reveals a large confor...	ACCEPT	Summary: Retain the curator-assigned lactose synthase activity with independent human biochemical support. The linked deposited lactose-synthase structures contain bovine galactosyltransferase and mouse alpha-lactalbumin; they explain the conserved acceptor switch but are not all-human structural experiments. Supporting Evidence: PMID:11419947 LA promotes the binding of glucose (Glc) to beta4Gal-T1
GO:0004461 lactose synthase activity	EXP PMID:806951 Lactose biosynthesis.	ACCEPT	Summary: Lactose synthase activity is established by independent human biochemical evidence. Retain the experimental GOA assertion with curator deference; this cached reference is classified as a review and has no abstract, so its original supporting content was not independently inspected.
GO:0005794 Golgi apparatus	IDA GO_REF:0000052	ACCEPT	Summary: Human Protein Atlas immunofluorescence (IDA) localizing B4GALT1 to the Golgi apparatus. Concordant with all other localization evidence. Core. Accept.
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	EXP PMID:29133956 Network inference from glycoproteomics data reveals new reac...	ACCEPT	Summary: Experimental demonstration of B4GALT1 galactosylation in the IgG glycosylation pathway (network inference plus enzymatic validation). Supports the core MF on complex N-glycans. Accept.
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	EXP PMID:37632720 Divergent Enzymatic Assembly of a Comprehensive 64-Membered ...	ACCEPT	Summary: Experimental use of B4GALT1 to galactosylate defined IgG N-glycans in a synthetic glycan library. Direct support for the core galactosyltransferase activity on N-glycan acceptors. Accept.
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	EXP PMID:38321209 Immobilized enzyme cascade for targeted glycosylation.	ACCEPT	Summary: Experimental demonstration of B4GALT1 galactosyltransferase activity in an immobilized enzyme cascade for targeted N-glycosylation. Core MF. Accept.
GO:0003945 N-acetyllactosamine synthase activity	EXP PMID:16157350 Oligosaccharide preferences of beta1,4-galactosyltransferase...	ACCEPT	Summary: Retain the curator-assigned free-GlcNAc N-acetyllactosamine synthase activity. Independent corroboration includes purified soluble human enzyme in PMID:33805 and the immobilized human GalT catalytic construct in PMID:38321209, whose activity with free GlcNAc was confirmed by MALDI-TOF MS/MS. The inspected PMID:16157350 abstract describes branched N-glycan acceptors; it does not independently verify every free-GlcNAc assay attributed to its full paper. Preserve the original EXP attribution with that access boundary. Supporting Evidence: PMID:16157350 PMID:33805 PMID:38321209 the activity of immobilized ... GalT ... was confirmed by MALDI-TOF MS/MS analysis ... GalT with free N-acetylglucosamine (GlcNAc)
GO:0004461 lactose synthase activity	EXP PMID:16157350 Oligosaccharide preferences of beta1,4-galactosyltransferase...	ACCEPT	Summary: Retain the curator-assigned lactose synthase activity, corroborated by human enzyme assayed with glucose and alpha-lactalbumin in PMID:33805. UniProt also assigns EC 2.4.1.22 to PMID:16157350, but its inspected abstract focuses on N-glycan acceptors; it does not expose the complete lactose-synthase assay evidence. Preserve the original EXP assertion without claiming those assays were independently read. Supporting Evidence: PMID:16157350 PMID:33805
GO:0005576 extracellular region	NAS PMID:2120039 Analysis of the substrate binding sites of human galactosylt...	KEEP AS NON CORE	Summary: The cited paper expressed a secreted human-enzyme fusion in E. coli; that construct does not itself demonstrate native human secretion. The extracellular assignment remains consistent with purified soluble enzyme from human fluids in PMID33805. Retain the NAS location with this source limitation.
GO:0005886 plasma membrane	EXP PMID:1714903 Evidence for a molecular distinction between Golgi and cell ...	KEEP AS NON CORE	Summary: The study supports relative enrichment of the long form at the plasma membrane in the examined systems. It does not establish that the long product is absent from the Golgi or that human products segregate exclusively between compartments. Retain contextual plasma-membrane localization. Supporting Evidence: PMID:1714903 the longer GalTase protein, ... is preferentially targeted to the plasma membrane, and the shorter GalTase protein resides primarily within the Golgi compartment.
GO:0009986 cell surface	EXP PMID:1714903 Evidence for a molecular distinction between Golgi and cell ...	KEEP AS NON CORE	Summary: Retain the documented surface localization without assigning it exclusively to a separate recognition function. Preferential targeting in the examined systems does not negate the Golgi pool of the long product.
GO:0061755 positive regulation of circulating fibrinogen levels	IMP PMID:34855475 Genetic and functional evidence links a missense variant in ...	KEEP AS NON CORE	Summary: Retain the experimental association between the p.Asn352Ser hypomorph and lower circulating fibrinogen as a non-core physiological phenotype. The same study reports reduced enzyme activity and altered serum-protein glycosylation. Its inspected abstract does not resolve the causal route connecting these observations, including possible secretion or clearance effects; the specific molecular core remains galactosyl transfer. Supporting Evidence: PMID:34855475 The mutant protein had 50% lower galactosyltransferase activity
GO:0006629 lipid metabolic process	IMP PMID:34855475 Genetic and functional evidence links a missense variant in ...	KEEP AS NON CORE	Summary: Retain the experimental LDL/lipid phenotype as a non-core physiological association: the p.Asn352Ser hypomorph is associated with lower LDL cholesterol alongside altered serum glycoprotein glycans and reduced enzyme activity. The inspected abstract does not establish the specific causal route. This IMP row records the systemic lipid phenotype, while the catalytic cores describe the directly established glycosyl-transfer reactions. Supporting Evidence: PMID:34855475
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	IMP PMID:34855475 Genetic and functional evidence links a missense variant in ...	ACCEPT	Summary: The p.Asn352Ser mutant shows ~50% reduced galactosyltransferase activity, providing mutant-phenotype support that B4GALT1 enables this activity. Core MF. Accept.
GO:0035250 UDP-galactosyltransferase activity	IMP PMID:34855475 Genetic and functional evidence links a missense variant in ...	MODIFY	Summary: Parent-level term (UDP-galactosyltransferase activity). The specific beta-1,4-galactosyltransferase activity is the experimentally established function; modify to the specific child. Proposed replacements: beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	IDA PMID:27872474 Multi-level glyco-engineering techniques to generate IgG wit...	ACCEPT	Summary: Direct assay: B4GALT1 used to galactosylate IgG Fc N-glycans in a glyco-engineering study. Supports the core MF. Accept.
GO:0005794 Golgi apparatus	IDA PMID:7744867 Golgi retention mechanism of beta-1,4-galactosyltransferase....	ACCEPT	Summary: Direct localization plus mechanism: transmembrane-domain-dependent homodimerization and tubulin association mediate Golgi retention. Core Golgi location. Accept. Supporting Evidence: PMID:7744867 Double mutations of these residues, Cys29-->Ser and His32-->Leu, abolish homodimerization and simultaneously reduce the Golgi retention.
GO:0030667 secretory granule membrane	TAS Reactome:R-HSA-6798743	KEEP AS NON CORE	Summary: Reactome neutrophil-degranulation pathway annotation. Reflects presence of B4GALT1 in granule-membrane proteomes during exocytosis rather than a core functional location. Keep as non-core.
GO:0035577 azurophil granule membrane	TAS Reactome:R-HSA-6798739	KEEP AS NON CORE	Summary: Reactome neutrophil azurophil-granule annotation, from large-scale granule proteomics. Not a core functional compartment for the galactosyltransferase. Keep as non-core.
GO:0070062 extracellular exosome	HDA PMID:23533145 In-depth proteomic analyses of exosomes isolated from expres...	KEEP AS NON CORE	Summary: Retain the curator-attributed extracellular-exosome detection from prostatic secretion proteomics as non-core. The exact supplementary protein hit was not independently verified, and exosome detection does not establish proteolytic shedding or an exosome-specific function.
GO:0016020 membrane	HDA PMID:19946888 Defining the membrane proteome of NK cells.	KEEP AS NON CORE	Summary: Retain the NK-cell membrane-proteome localization with curator deference. A broad experimentally supported membrane location is not over-annotation; refining it solely to Golgi would potentially erase surface-membrane scope. Exact supplementary B4GALT1 hit was not independently reverified.
GO:0005576 extracellular region	HDA PMID:16502470 Human colostrum: identification of minor proteins in the aqu...	KEEP AS NON CORE	Summary: Retain extracellular detection in human colostrum proteomics as non-core. Independent human biochemistry establishes soluble active enzyme in milk, but this proteomics assertion alone does not distinguish cleavage state or every extracellular molecular form.
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	IDA PMID:16157350 Oligosaccharide preferences of beta1,4-galactosyltransferase...	ACCEPT	Summary: Human wild-type enzyme kinetics and M340H structures support recognition and galactosylation of branched N-glycan GlcNAc acceptors. The 1,2-1,6-arm trisaccharide has an approximately tenfold lower Km than the 1,2-1,3-arm and 1,4-1,3-arm trisaccharides. This directly supports the core glycopeptide galactosyltransferase activity; the mutant soluble construct is not treated as full-length native enzyme. Supporting Evidence: PMID:16157350 With the wild-type ... K(m) of 1,2-1,6-arm is approximately tenfold lower than for 1,2-1,3-arm and 1,4-1,3-arm
GO:0006487 protein N-linked glycosylation	IDA PMID:16157350 Oligosaccharide preferences of beta1,4-galactosyltransferase...	ACCEPT	Summary: Direct-assay support for B4GALT1's role in N-glycan maturation (galactosylation of N-glycan antennae). Core process. Accept. Supporting Evidence: PMID:16157350 transfers galactose ... branched N-linked oligosaccharide chains of glycoproteins
GO:0030145 manganese ion binding	IDA PMID:16157350 Oligosaccharide preferences of beta1,4-galactosyltransferase...	ACCEPT	Summary: Retain manganese binding as the catalytic-cofactor component of the galactosyltransferase core. UniProt identifies Mn2+ as cofactor, and the deposited human M340H soluble construct contains modeled Mn. The paper abstract itself does not describe the metal coordination, and this structure does not establish a physiological full-length oligomer. Manganese is integrated into the catalytic core rather than represented as an additional standalone binding core. Supporting Evidence: PMID:16157350 file:human/B4GALT1/B4GALT1-uniprot.txt
GO:0070062 extracellular exosome	HDA PMID:19199708 Proteomic analysis of human parotid gland exosomes by multid...	KEEP AS NON CORE	Summary: Retain the curator-attributed parotid-exosome detection as a contextual non-core location. The exact supplementary hit was not independently verified; the location does not by itself identify a shed catalytic domain.
GO:0070062 extracellular exosome	HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos...	KEEP AS NON CORE	Summary: Retain the curator-attributed urinary-exosome detection as a contextual non-core location. The abstract-only cache does not independently verify the exact protein hit or its cleavage state.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-3656230	ACCEPT	Summary: Reactome places the (defective) keratan-galactosylation reaction at the Golgi membrane. Correct core location. Accept.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-4793956	ACCEPT	Summary: Reactome Golgi membrane location for the N-glycan galactosylation reaction. Correct core location. Accept.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-9035949	ACCEPT	Summary: Reactome Golgi membrane location (N-glycan precursor reaction). Correct core location, redundant with the other Golgi membrane annotations. Accept.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-9035950	ACCEPT	Summary: Reactome Golgi membrane location (keratan branch reaction). Correct core location. Accept.
GO:0005886 plasma membrane	TAS Reactome:R-HSA-1297338	KEEP AS NON CORE	Summary: The Reactome fertilization event places B4GALT1 in a surface-recognition context. Retain its plasma-membrane location as non-core; the pathway summary and mouse-derived UniProt functional statements do not independently establish every mechanistic detail in human sperm.
GO:0005886 plasma membrane	TAS Reactome:R-HSA-6798739	KEEP AS NON CORE	Summary: Reactome neutrophil-degranulation pathway (plasma-membrane fusion of azurophil granules). Non-core trafficking location. Keep as non-core.
GO:0005886 plasma membrane	TAS Reactome:R-HSA-6798743	KEEP AS NON CORE	Summary: Reactome secretory-granule exocytosis pathway. Non-core trafficking location. Keep as non-core.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-2025723	ACCEPT	Summary: Reactome Golgi membrane location ("B4GALTs transfer Gal to the N-glycan precursor"). Correct core location. Accept.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-2046265	ACCEPT	Summary: Reactome Golgi membrane location ("B4GALTs transfer Gal to the keratan chain"). Correct core location. Accept.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-2046298	ACCEPT	Summary: Reactome Golgi membrane location ("B4GALTs transfer Gal to a branch of keratan"). Correct core location. Accept.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-5653878	ACCEPT	Summary: Reactome Golgi membrane location for "B4GALT1:LALBA transfers Gal from UDP-Gal to Glc to form Lac" (lactose synthesis occurs in the Golgi). Correct core location. Accept.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-5653886	ACCEPT	Summary: Reactome Golgi membrane location for "B4GALT1 binds LALBA". Correct core location (lactose synthase assembly in the Golgi). Accept.
GO:0000139 Golgi membrane	TAS Reactome:R-HSA-975919	ACCEPT	Summary: Reactome Golgi membrane location ("Addition of galactose by beta 4-galactosyltransferases"). Correct core location. Accept.
GO:0003945 N-acetyllactosamine synthase activity	IDA PMID:2120039 Analysis of the substrate binding sites of human galactosylt...	ACCEPT	Summary: Protein-engineering/mutagenesis study of recombinant human galactosyltransferase mapping the GlcNAc and UDP-Gal binding residues (Tyr284, Tyr309, Trp310). Directly supports the core LacNAc-synthase activity. Accept. Supporting Evidence: PMID:2120039 Tyr284, Tyr309 and Trp310 are critically involved in the N-acetyglucosamine binding and Tyr309 is involved in UDP-galactose binding
GO:0005794 Golgi apparatus	IDA PMID:10900002 Localization of alpha 1,3-fucosyltransferase VI in Weibel-Pa...	ACCEPT	Summary: The cached abstract explicitly reports beta4-galactosyltransferase-1 colocalization in human endothelial Golgi, despite the paper focusing on fucosyltransferase VI. This supports the core location. The available body contains Abstract and Discussion, not complete Methods and Results.
GO:0009312 oligosaccharide biosynthetic process	IDA PMID:2120039 Analysis of the substrate binding sites of human galactosylt...	ACCEPT	Summary: This is already oligosaccharide biosynthetic process, not its metabolic parent. Formation of oligosaccharides is directly catalytic and core. The abstract-only recombinant-enzyme source does not warrant forcing every measured acceptor into an N-linked protein-specific process.
GO:0000138 Golgi trans cisterna	IDA PMID:6121819 Immunocytochemical localization of galactosyltransferase in ...	ACCEPT	Summary: Immuno-EM directly localizing galactosyltransferase to two-to-three trans cisternae of the Golgi, codistributing with thiamine pyrophosphatase. This is the most specific, experimentally supported core sub-Golgi location. Accept. Supporting Evidence: PMID:6121819 Label by gold particles was limited to two to three trans cisternae of the Golgi apparatus
GO:0003831 beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity	IDA PMID:33805 The charge heterogeneity of soluble human galactosyltransfer...	ACCEPT	Summary: Purified soluble human galactosyltransferase from milk/amniotic fluid/ascites shows Gal transfer to GlcNAc/glycoprotein acceptors. Direct support for the core MF (the soluble form retains activity). Accept. Supporting Evidence: PMID:33805 ovalbumin, sialic-acid-free ovine submaxillary mucin ... were used as acceptor substrates.
GO:0003945 N-acetyllactosamine synthase activity	IDA PMID:33805 The charge heterogeneity of soluble human galactosyltransfer...	ACCEPT	Summary: Same purified enzyme assayed with free N-acetylglucosamine acceptor (LacNAc synthesis). Direct support for the core LacNAc-synthase facet. Accept. Supporting Evidence: PMID:33805 All enzyme forms showed similar activity when free N-acetylglucosamine
GO:0004461 lactose synthase activity	IDA PMID:33805 The charge heterogeneity of soluble human galactosyltransfer...	ACCEPT	Summary: Same enzyme assayed with glucose acceptor in the presence of alpha-lactalbumin (lactose synthase activity). Direct support for the core bifunctional activity. Accept. Supporting Evidence: PMID:33805 glucose, in the presence of alpha-lactalbumin file:human/B4GALT1/B4GALT1-uniprot.txt Reaction=D-glucose + UDP-alpha-D-galactose = lactose
GO:0009897 external side of plasma membrane	IDA PMID:3917437 Immunocytochemical demonstration of ecto-galactosyltransfera...	KEEP AS NON CORE	Summary: Immuno-EM of human duodenal enterocytes showing ecto-galactosyltransferase preferentially oriented to the outer surface of the plasma membrane. Genuine surface (ecto) pool; specialized/non-core relative to the Golgi catalytic role. Keep as non-core. Supporting Evidence: PMID:3917437 preferential orientation to the outer surface of the plasma membrane
GO:0016323 basolateral plasma membrane	IDA PMID:3917437 Immunocytochemical demonstration of ecto-galactosyltransfera...	KEEP AS NON CORE	Summary: Immuno-EM in human duodenal enterocytes detects lateral plasma-membrane labeling, with intensely labeled membrane interdigitations. Retain this contextual basolateral location as non-core relative to Golgi catalysis. The proposed adhesion role is a hypothesis and is not the evidence for the location. Supporting Evidence: PMID:3917437 lateral plasma membrane ... interdigitations were intensely labeled.
GO:0030057 desmosome	IDA PMID:3917437 Immunocytochemical demonstration of ecto-galactosyltransfera...	KEEP AS NON CORE	Summary: Retain the curator-assigned desmosomal localization, bounded to human enterocyte immuno-EM. The official GO term is a cellular component; no dedicated desmosomal function is required. Cached abstract mentions junctional complexes but exact desmosome image/full text was not independently read.
GO:0031526 brush border membrane	IDA PMID:3917437 Immunocytochemical demonstration of ecto-galactosyltransfera...	KEEP AS NON CORE	Summary: Intense brush-border-membrane labeling of absorptive enterocytes (ecto-GalT). A genuine apical surface pool in this cell type; specialized/non-core. Keep as non-core. Supporting Evidence: PMID:3917437 most intense labeling ... along the brush border membrane
GO:0035250 UDP-galactosyltransferase activity	IDA PMID:3917437 Immunocytochemical demonstration of ecto-galactosyltransfera...	MODIFY	Summary: Parent-level activity term inferred from ecto-GalT enzymatic detection. The specific beta-1,4-galactosyltransferase activity is established; modify to the specific child. Proposed replacements: beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity
GO:0009312 oligosaccharide biosynthetic process	NAS PMID:7540104 Analysis of the sequences of human beta-1,4-galactosyltransf...	ACCEPT	Summary: Retain the oligosaccharide biosynthesis annotation: B4GALT1 performs the galactosyl-transfer step forming N-acetyllactosamine and, with alpha-lactalbumin, lactose. These disaccharide products give a positive chemical basis for the process term across catalytic contexts. PMID:33805 independently corroborates both acceptor activities. Preserve the original NAS attribution to the cDNA paper; its abstract is not an independently inspected enzyme assay. Supporting Evidence: PMID:7540104 PMID:33805
GO:0008378 galactosyltransferase activity	NAS PMID:7540104 Analysis of the sequences of human beta-1,4-galactosyltransf...	MODIFY	Summary: Refine this general galactosyltransferase assertion to the already represented substrate-specific activities: glycopeptide terminal-GlcNAc galactosylation, free-GlcNAc N-acetyllactosamine synthesis, and glucose-dependent lactose synthesis in association with alpha-lactalbumin. Human enzyme studies independently support these contexts. Preserve the cDNA paper NAS attribution without claiming it assayed all three reactions; the replacements introduce no NEW assertion. Proposed replacements: beta-N-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase activity N-acetyllactosamine synthase activity lactose synthase activity Supporting Evidence: PMID:7540104 PMID:16157350 PMID:33805

Gene Description

Proposed New Ontology Terms

lactose synthase complex

Existing Annotations Review

Core Functions

Transfers galactose from UDP-galactose to terminal GlcNAc residues of protein-linked N-glycans in the Golgi, supporting complex N-glycan maturation. Catalysis requires manganese; the enzyme occupies trans cisternae and can occur more broadly across Golgi stacks.

Transfers galactose from UDP-galactose to free N-acetylglucosamine to form N-acetyllactosamine, a substrate-specific facet of the manganese-dependent catalytic activity.

In a 1:1 complex with alpha-lactalbumin in lactating mammary cells, transfers galactose from UDP-galactose to glucose to synthesize lactose. Alpha-lactalbumin promotes glucose binding and changes acceptor preference, enabling this tissue-specific catalytic role at the Golgi.

References

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Notes

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