Center for Bioinformatics
Oxidoreductases | Transferases | Hydrolases | Lyases | Isomerases | Ligases

Basic Information

Enzyme Number

2.4.1.22

Official Name

lactose synthase

Name from literature

galactosyltransferase

Pathway from literature

uridine nucleotide cycle that supports lactose synthesis

Pathway from KEGG

Carbohydrate Metabolism; Galactose metabolism; map00052

Organisms

Human (9606)

Genome localization

1p34-p33[8704 ], 9p13[2683 ], 12q13[3906 ],

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-galactose to N-acetylglucosamine (EC 2.4.1.90 N-acetyllactosamine synthase).

Rate-limiting Description

"Decreased sialylation correlated with an increase in N-linked carbohydrates missing terminal galactose moieties, suggesting that beta-1,4- galactosyltransferase may be rate limiting in our system." (16937399)

"Together, these results strongly suggest that galactosylation of I-branch is a rate-limiting step in I-branched poly-N-acetyllactosamine synthesis, allowing poly-N-acetyllactosamine extension mostly along the linear poly-N-acetyllactosamine side chain." (10092606)

Regulatory Information

Upstream transcription factor

7157;6927

Regulatory type

Detail

others;

"Hormonal induction and regulation of lactose synthetase in mouse mammary gland." (5808320)

transcriptional factor;HNF1alpha(6927)

"TNFalpha modulates the glycosylation of endothelial cells by a mechanism that directly enhances the stability of beta4GalT-1 mRNA transcripts" (15668241)

transcriptional factor;HNF1alpha(6927)

"TNFalpha modulates the glycosylation of endothelial cells by a mechanism that directly enhances the stability of beta4GalT-1 mRNA transcripts" (15668241)

transcriptional factor;p53(7157)

"results suggested that beta1,4GalT II might serve as a target gene of p53 transcription factor during adriamycin-induced HeLa cell apoptosis, which elucidated a new mechanism of p53-mediated cell apoptosis" (18211920)

transcriptional factor;p53(7157)

"results suggested that beta1,4GalT II might serve as a target gene of p53 transcription factor during adriamycin-induced HeLa cell apoptosis, which elucidated a new mechanism of p53-mediated cell apoptosis" (18211920)

Gene ontology

Gene ontology

GO:0009897 (C) external side of plasma membrane [P15291 ];
GO:0030145 (F) manganese ion binding [O60909, P15291 ];
GO:0030112 (C) glycocalyx [P15291 ];
GO:0009312 (P) oligosaccharide biosynthetic process [P15291 ];
GO:0005794 (C) Golgi apparatus [O60909 ];
GO:0005975 (P) carbohydrate metabolic process [O60909 ];
GO:0031526 (C) brush border membrane [P15291 ];
GO:0003945 (F) N-acetyllactosamine synthase activity [O60909, P15291 ];
GO:0005576 (C) extracellular region [P15291 ];
GO:0003831 (F) beta-N-acetylglucosaminylglycopeptide beta-... [O60909, P15291 ];
GO:0016021 (C) integral to membrane [O60909, P15291 ];
GO:0004461 (F) lactose synthase activity [O60909, P15291 ];
GO:0016323 (C) basolateral plasma membrane [P15291 ];
GO:0030057 (C) desmosome [P15291 ];
GO:0000138 (C) Golgi trans cisterna [P15291 ];

Tissue expression

Tissue From HPRD

Thymus [04928 ];
Colon [04928 ];
Uterus [04928 ];
Spinal cord [04928 ];
Salivary gland [04928 ];
Fetus [04928 ];
Leukocyte [04928 ];
Intestine [04928 ];
Testis [04928 ];
Skeletal muscle [04928 ];
Liver [04928, 00659 ];
Muscle [04928 ];
Brain [04928 ];
Spleen [04928 ];
Prostate [04928 ];
Kidney [04928 ];
Mammary gland [04928, 01024 ];
Adrenal gland [04928 ];
Heart [04928 ];
Lung [04928 ];
Ovary [04928 ];
Pancreas [04928 ];
Trachea [04928 ];
Milk [01024 ];
Placenta [04928, 00659 ];
Thyroid gland [04928 ];
Stomach [04928 ];

Tissue specificity

Ubiquitously expressed, but at very low levels in fetal and adult brain [P15291 ];

Weakly expressed in various tissues. Highest expression in prostate, testis, ovary, intestine, muscle, and in fetal brain [O60909 ];

Subcellular localization

Localization

extracellular matrix [P15291 ];

extracellular [P15291 ];

golgi apparatus [O60909, P15291 ];

membrane [O60909, P15291 ];

Disease relevance

Disease

Defects in B4GALT1 are the cause of congenital disorder of glycosylation type 2D (CDG2D) [MIM:607091]. CDGs are a family of severe inherited diseases caused by a defect in protein N-glycosylation. They are characterized by under-glycosylated serum proteins. These multisystem disorders present with a wide variety of clinical features, such as disorders of the nervous system development, psychomotor retardation, dysmorphic features, hypotonia, coagulation disorders, and immunodeficiency. The broad spectrum of features reflects the critical role of N-glycoproteins during embryonic development, differentiation, and maintenance of cell functions [P15291 ];

Links

SwissProt

O60909; P15291

Entrez Gene

2683; 3906; 8704

HPRD

00659; 04928; 01024



  Copyright 2009, Center for Bioinformatics 
  Last Modified: 2009-03-24  
  Design by Zhao Min