Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The specificity of glycosyltransferases is a major control factor in the biosynthesis of O-glycans. The enzyme that synthesizes O-glycan core 1, i.e., UDP-galactose:N-acetylgalactosamine-alpha-R beta 3-galactosyltransferase (beta 3-Gal-T; EC 2.4.1.122), was partially purified from rat liver. The enzyme preparation, free of pyrophosphatases, beta 4-galactosyltransferase, beta-galactosidase, and N-acetylglucosaminyltransferase I, was used to study the specificity and inhibition of the beta 3-Gal-T. beta 3-Gal-T activity is sensitive to changes in the R-group of the GalNAc alpha-R acceptor substrate and is stimulated when the R-group is a peptide or an aromatic group. Derivatives of GalNAc alpha-benzyl were synthesized and tested as potential substrates and inhibitors. Removal or substitution of the 3-hydroxyl or removal of the 4-hydroxyl of GalNAc abolished beta 3-Gal-T activity. Compounds with modifications of the 3- or 4-hydroxyl of GalNAc alpha-benzyl did not show significant inhibition. Removal or substitution of the 6-hydroxyl of GalNAc reduced activity slightly and these derivatives acted as competitive substrates. derivatives with epoxide groups attached to the 6-position of GalNAc acted as substrates and not as inhibitors, with the exception of the photosensitive 6-O-(4,4-azo)pentyl-GalNAc alpha-benzyl, which inhibited Gal incorporation into GalNAc alpha-benzyl. The results indicate that the enzyme does not require the 6-hydroxyl of GalNAc, but needs the 3- and the axial 4-hydroxyl as essential requirements for binding and activity. In the usual biochemical O-glycan pathway, core 2 (GlcNAc beta 6[Gal beta 3] GalNAc alpha-) is formed from core 1 (Gal beta 3GalNAc-R). We have now demonstrated an alternate pathway that may be of importance in human tissues.
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PMID:Control of O-glycan synthesis: specificity and inhibition of O-glycan core 1 UDP-galactose:N-acetylgalactosamine-alpha-R beta 3-galactosyltransferase from rat liver. 151 Aug 30

We inserted a full-length murine cDNA, which had been isolated from F9 embryonal carcinoma cells by using a bovine lactose synthetase A protein cDNA as a probe, in a mammalian expression vector (pCMGT1) and expressed it in COS-1 cells to characterize the pCMGT1-directed enzyme. The galactosyltransferase activity toward asialo-agalacto-transferrin (AsAg-Tf) in the pCMGT1-transfected cells was approximately eightfold higher than that in mock- or non-transfected cells. In contrast, no difference was observed in the specific activity of galactose transfer between pCMGT1-transfected cells and mock- or non-transfected cells when asialo-ovine submaxillary mucin were used as an acceptor. Since almost all [3H]galactose incorporated into the AsAg-Tf was released by digestion with streptococcal beta-galactosidase, most of the linkage created by this enzyme was in the Gal beta 1-4GlcNAc group. The acceptor specificity of the pCMGT1-directed enzyme was changed from N-acetylglucosamine to glucose by adding alpha-lactalbumin in the reaction mixture. Alpha-Lactalbumin also partially inhibited the galactose transfer to AsAg-Tf. The kinetic study revealed that the apparent Km values of the pCMGT1-directed enzyme for N-acetylglucosamine, AsAg-Tf and UDP-Gal are 2 mM, 60 microM and 24 microM, respectively. These results indicated that the murine cDNA isolated from F9 cells encodes an active enzyme which catalyzes not only the lactose synthesis but also the transfer of galactose to N-acetylglucosamine residues of Asn-linked sugar chains of glycoproteins in a beta 1-4 linkage.
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PMID:Characterization of a murine beta 1-4 galactosyltransferase expressed in COS-1 cells. 170 63

1. The following fractions were prepared from rat kidney and characterized ultrastructurally, biochemically and enzymically: (a) an ordinary rough microsomal (RM(1)) fraction; (b) a special rough microsomal (RM(2)) fraction enriched seven- to nine-fold in acid hydrolases over the homogenate; (c) a smooth microsomal (SM) fraction; (d) a Golgi (GM) fraction enriched 2.5-fold in acid hydrolases and 10-, 15- and 20-fold in sialyltransferase, N-acetyl-lactosamine synthetase and galactosyltransferase respectively; (e) a lysosomal (L) fraction enriched 15- to 23-fold in acid hydrolases. The frequency of Golgi sacs and tubules seen in the electron microscope and the specific activity of the three glycosyltransferases in these fractions increased in the order: RM(2)<RM(1)<SM<GM. 2. Five lysosomal hydrolases, acid phosphatase, beta-N-acetyl-hexosaminidase, beta-galactosidase, beta-glucuronidase and arylsulphatase, were characterized in these fractions with respect to (a) solubility on freeze-thawing and (b) electrophoretic mobility in polyacrylamide gels. 3. In the RM(2) fraction each of these hydrolases occurred largely or exclusively as a single bound basic form coincident with cationic glycoprotein bands in gels (Goldstone et al., 1973). 4. In the L fraction these hydrolases were present largely as soluble, acidic (anionic) forms. 5. The solubility, electrophoretic heterogeneity and anodic mobility of these hydrolases increased progressively in subcellular fractions in the order: RM(2)<RM(1)<SM<GM<L. 6. These findings, together with evidence cited in the text showing that N-acetylneuraminic acid residues are responsible for the solubility and electronegative charge of these acidic forms and incorporation of these residues into the Golgi apparatus, support the following scheme for the biosynthesis of lysosomal enzymes. Each hydrolase is synthesized as a bound basic glycoprotein enzyme in a restricted portion of the rough endoplasmic reticulum. The soluble, acidic forms are generated as the nascent glycoprotein enzymes migrate through the Golgi apparatus through the attachment of sugar sequences containing N-acetylneuraminic acid.
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PMID:Physicochemical modifications of lysosomal hydrolases during intracellular transport. 472 40

In previous studies on glycosyltransferase activities in porcine trachea, we demonstrated the presence of two galactosyltransferases which transfer galactose from UDP-galactose to N-acetylglucosamine (Sheares, B.T. and Carlson, D.M. (1983) J. Biol. Chem. 258, 9893-9898). One enzyme, UDP-galactose:N-acetylglucosamine 3 beta-galactosyltransferase, synthesized galactosyl-beta 1,3-N-acetylglucosamine while the other, UDP-galactose:N-acetylglucosamine 4 beta-galactosyltransferase, synthesized galactosyl-beta 1,4-N-acetylglucosamine. A third galactosyltransferase has now been demonstrated utilizing a solubilized membrane preparation from pig trachea, which also synthesizes galactosyl-beta 1,4-N-acetylglucosamine as determined by gas-liquid chromatography and Diplococcus pneumoniae beta-galactosidase treatment. This new UDP-galactose:N-acetylglucosamine 4 beta-galactosyltransferase is distinct from the lactose synthetase A protein in that it does not bind to alpha-lactalbumin-agarose or to N-acetylglucosamine-agarose. The enzyme is separable from the UDP-galactose:N-acetylgalactosaminyl-mucin 3 beta-galactosyltransferase by affinity chromatography on asialo ovine submaxillary mucin adsorbed to DEAE-Sephacel. This newly discovered 4 beta-galactosyltransferase binds to UDP-hexanolamine-Sepharose and is partially separated from UDP-galactose:N-acetylglucosamine 3 beta-galactosyltransferase by Sephacryl S-200 gel filtration chromatography. Neither high concentrations of N-acetylglucosamine (200 mM) nor alpha-lactalbumin inhibits the incorporation of galactose into galactosyl-beta 1,4-N-acetylglucosamine by this enzyme.
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PMID:Two distinct UDP-galactose: 2-acetamido-2-deoxy-D-glucose 4 beta-galactosyltransferases in porcine trachea. 642 38

A high galactosyltransferase activity with lactotriaosylceramide as acceptor has been found in human serums. The reaction requires UDP-galactose, Mn2+, and Triton X-100. It has a pH optimum of 6.0 and a Km for lactotriaosylceramide of 0.66 mM. On the basis of methylation analysis and susceptibility towards beta-galactosidase the reaction product has been identified as neolactotetraosylceramide. Lactotetraosylceramide formation was not observed. Evidence is presented that the serum enzymic activity can be attributed to N-acetyllactosamine synthase (EC 2.4.1.90). The beta 1 leads to 4-galactosyltransferase activities with lactotriaosylceramide as acceptor have been determined in different human sera. The activity is independent of ABO, p and Rh blood-group status. The enzyme is within a normal range in serums of cancer patients.
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PMID:Enzymatic synthesis of neolactotetraosylceramide by the N-acetyllactosamine synthase of human serum. 681 Dec 67

Antibodies against Leishmania major wheat germ agglutinin-binding glycoproteins were used to select from a genomic lambda gt11 expression library a clone coding for a L. major glycoprotein. The partial DNA sequence indicated the presence of a mosaic of repetitive sequences. Southern blot hybridisation on genomic DNA using the cloned gene as a probe at high stringency suggested a single gene, which was localised to chromosome band 18. Northern blot analysis of L. major mRNA detected a major transcript of 7.5 kb and a minor 4.0-kb transcript. Antibodies affinity-purified on the fusion protein identified a complex of two water-soluble cytoplasmic polypeptides of approximately 96 kDa and 92 kDa in L. major promastigotes and amastigotes. They also recognised polypeptides in other Leishmania species, in Crithidia lucilliae and very weakly in Leptomonas. The apparent molecular weight of these polypeptides, while conserved within each species, varied between species. A peptide map of the two polypeptides from L. major generated an identical pattern suggesting a close relatedness at the protein level. This protein complex was not hydrolysed by N-glycanase and was not affected by tunicamycin, but treatment with anhydrous hydrogen fluoride suggested that it is O-glycosylated. The glycan moiety appears to be N-acetylglucosamine, and N-acetylglucosamine beta-1,4-galactosyltransferase was capable of adding [3H]galactose to it. This was susceptible to beta elimination and beta-galactosidase treatment. Taken together, the data indicates that gp96/92 belongs to the newly described class of cytoplasmic and nuclear glycoproteins containing O-linked N-acetylglucosamine.
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PMID:Identification, characterisation and genomic cloning of a O-linked N-acetylglucosamine-containing cytoplasmic Leishmania glycoprotein. 811 27