Lactose synthesis (Homo sapiens)

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Bibliography

1. Findlay JB, Brew K.; ''The complete amino-acid sequence of human -lactalbumin.''; PubMed Europe PMC Scholia
2. Brew K, Hill RL.; ''Lactose biosynthesis.''; PubMed Europe PMC Scholia
3. Andrews P.; ''Purification of lactose synthetase a protein from human milk and demonstration of its interaction with alpha-lactalbumin.''; PubMed Europe PMC Scholia
4. Nemeth BA, Tsang SW, Geske RS, Haney PM.; ''Golgi targeting of the GLUT1 glucose transporter in lactating mouse mammary gland.''; PubMed Europe PMC Scholia
5. Ramakrishnan B, Qasba PK.; ''Crystal structure of lactose synthase reveals a large conformational change in its catalytic component, the beta1,4-galactosyltransferase-I.''; PubMed Europe PMC Scholia

History

External references

DataNodes

Name	Type	Database reference	Comment
B4GALT1	Protein	P15291 (Uniprot-TrEMBL)
B4GALT1:LALBA	Complex	R-HSA-5653885 (Reactome)
B4GALT1	Protein	P15291 (Uniprot-TrEMBL)
Glc	Metabolite	CHEBI:17925 (ChEBI)
LALBA	Protein	P00709 (Uniprot-TrEMBL)
LALBA	Protein	P00709 (Uniprot-TrEMBL)
Lac	Metabolite	CHEBI:17716 (ChEBI)
Mn2+	Metabolite	CHEBI:29035 (ChEBI)
SLC2A1	Protein	P11166 (Uniprot-TrEMBL)
SLC2A1 tetramer	Complex	R-HSA-5653881 (Reactome)
UDP-Gal	Metabolite	CHEBI:18307 (ChEBI)
UDP	Metabolite	CHEBI:17659 (ChEBI)

Annotated Interactions

Source	Target	Type	Database reference	Comment
	B4GALT1:LALBA	Arrow	R-HSA-5653886 (Reactome)
B4GALT1:LALBA		mim-catalysis	R-HSA-5653878 (Reactome)
B4GALT1			R-HSA-5653886 (Reactome)
	Glc	Arrow	R-HSA-5653873 (Reactome)
Glc			R-HSA-5653873 (Reactome)
Glc			R-HSA-5653878 (Reactome)
LALBA			R-HSA-5653886 (Reactome)
	Lac	Arrow	R-HSA-5653878 (Reactome)
Mn2+		Arrow	R-HSA-5653886 (Reactome)
			R-HSA-5653873 (Reactome)	SLC2A1 (aka GLUT1) tetramer in the Golgi membrane mediates the facilitated diffusion of glucose from the cytosol into the Golgi lumen. SLC2A1, normally confined to the plasma membrane, is also abundant in the Golgi membranes of epithelial cells of the lactating mammary gland, as demonstrated experimentally in mice (Nemeth et al. 2000). It is not known how this physiological state-specific relocalization is regulated.
			R-HSA-5653878 (Reactome)	In the Golgi membrane, the B4GALT1 subunit of the B4GALT1:LALBA (beta-1,4-galactosyltransferase 1 : alpha-lactalbumin) complex catalyzes the transfer of galactose from UDP-galactose to free glucose to form galactose and UDP (Andrews 1970; Ramakrishnan & Qasba 2001). The representation here of a stable protein complex catalyzing the transformation of small molecule substrates provides a simplified view of the true reaction mechanism (Brew and Hill 1975), but is sufficient to identify the key participating molecules and their roles.
			R-HSA-5653886 (Reactome)	B4GALT1 (beta-1,4-galactosyltransferase 1) in the Golgi membrane associates with LALBA (alpha-lactalbumin) to form a heterodimer. This binding reaction is positively regulated by Mn2+ ions and UDP-galactose. This heterodimer has been observed both in solution in vitro and in crystalline form (Andrews 1970; Ramakrishnan & Qasba 2001). The galactosyltransferase enzyme is found in the Golgi membrane of many cell types. LALBA is expressed specifically in the lactating mammary gland. Binding LALBA modulates the specificity of the galactosyltransferase enzyme. Alone, B4GALT1 transfers galactose moieties to glycolipids and N-linked oligosaccharides of glycoproteins. Complexed with LALBA, it transfers galactose to free glucose to form lactose (Brew and Hill 1975).
SLC2A1 tetramer		mim-catalysis	R-HSA-5653873 (Reactome)
UDP-Gal		Arrow	R-HSA-5653886 (Reactome)
UDP-Gal			R-HSA-5653878 (Reactome)
	UDP	Arrow	R-HSA-5653878 (Reactome)