Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

A cDNA clone for a monosaccharide transporter (MST1) was isolated from tobacco, which is most strongly expressed in the various sink tissues of mature tobacco plants: roots, flowers, and young leaves. An open reading frame of 1569 bp codes for a protein with 523 amino acids and a calculated molecular weight of 57,717 Da. The protein is homologous to a group of other plant monosaccharide transport proteins from Arabidopsis thaliana and Chlorella kessleri, to human glucose transporters and to Saccharomyces cerevisiae and several bacterial sugar transport proteins. As with these other transporters, the MST1 protein is extremely lipophilic and has 12-putative membrane-spanning domains. Heterologous expression of the MST1 cDNA clone in Saccharomyces cerevisiae allowed its characterization as a putative H+/monosaccharide co-transporter, catalyzing the uptake of hexoses (e.g. D-glucose and D-galactose) or pentoses (e.g. D-xylose) and the energy dependent and uncoupler sensitive accumulation of non-metabolizable substrates (e.g. D-xylose or 3-O-methyl-glucose). Polyclonal antibodies were raised against a fusion protein of beta-galactosidase and the last 27 amino acids of the C-terminus of the MST1 protein. In SDS extracts of transformed yeast cells these antibodies recognize a polypeptide with an apparent molecular weight of 42 kDa, which is absent in extracts from untransformed control cells.
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PMID:A sink-specific H+/monosaccharide co-transporter from Nicotiana tabacum: cloning and heterologous expression in baker's yeast. 825 64

Rhamnogalacturonan I (RG-I) has been isolated from the walls of suspension-cultured sycamore cells (Acer pseudoplatanus), and additional structural features of the polysaccharide were elucidated. Treatment of RG-I with a purified endo-(1-->5)-alpha-L-arabinanase released a series of arabinose-containing oligosaccharides with degrees of polymerization (dp's) between 2 and 20. These oligosaccharides were shown, by glycosyl-linkage composition analysis, to contain terminal, 5-, and (3-->5)-linked Araf residues. These results provide evidence that a branched arabinan is attached to the backbone of RG-I. RG-I was freed of 95% of its arabinosyl residues by treating the polysaccharide with a combination of endo-(1-->5)-alpha-L-arabinanase and alpha-L-arabinosidase. No galacturonic acid was released by these enzymes, which is evidence that the arabinosyl-containing portions of the side chains do not contain galactosyluronic acid residues. The galactose-containing portions of the side chains of RG-I were not fragmented by an endo-(1-->4)-beta-D-galactanase. However, approximately 85% of the galactose and small amounts of galacturonic acid were released by digestion of arabinose-depleted RG-I with a combination of endo- and exo-beta-D-galactanases. The galacturonic acid may have been released by small amounts of an exo-alpha-galactosyluronidase contaminating the galactanases. Treatment of RG-I with this mixture of endo- and exo-glycanases resulted in a relatively size-homogeneous, almost side chain-free backbone composed of the O-acetylated diglycosyl repeating unit -->4)-alpha-D-GalpA-(1-->2)-alpha-L-Rhap. A combination of 1H NMR spectroscopy and periodate oxidation established that the backbone repeating unit contained a single O-acetyl substituent on C-2 or C-3 of each galactosyluronic acid residue.
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PMID:Structural characterization of endo-glycanase-generated oligoglycosyl side chains of rhamnogalacturonan I. 834 45

Actinomyces viscosus T14V, a Gram-positive bacterium found in the oral cavity, was found to be insensitive to glucose-mediated catabolite repression. Basal levels of beta-galactosidase (18-26 U) were observed at all phases of growth regardless of the culture conditions. Further, beta-galactosidase could not be induced with lactose, or with a known inducer of the enzyme, isopropyl-beta-D-thiogalactoside, or with dibutyryl cAMP. Glucose, on the other hand, stimulated cAMP accumulation in a concentration-dependent manner. Fructose and sucrose mimicked the effects of glucose on cAMP accumulation, whereas galactose, mannose and maltose had lesser stimulatory effects. Other carbon sources, i.e., lactose, alpha-methylglucoside, ribose, xylose and succinate were without effect. Glucose and alpha-methylglucoside were found to stimulate cAMP accumulation in toluene-permeabilized cells, in the presence of the phosphodiesterase inhibitor, theophylline. Glucose did not stimulate cAMP levels in other Gram-positive bacteria including Streptococcus mutans, S. sanguis and S. salivarius but did cause cAMP accumulation in other strains of A. viscosus. The results suggest that glucose effects on cAMP metabolism are independent of the induction of beta-galactosidase as presently defined for Escherichia coli, and that the effects appear to be selective to the A. viscosus bacteria. The results also suggest that glucose stimulates cAMP accumulation via activation of adenylate cyclase.
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PMID:Glucose stimulates cAMP accumulation in the oral bacterium Actinomyces viscosus. 839 89

The AraC protein, which regulates the L-arabinose operons in Escherichia coli, was dissected into two domains that function in chimeric proteins. One provides a dimerization capability and binds the ligand arabinose, and the other provides a site-specific DNA-binding capability and activates transcription. In vivo and in vitro experiments showed that a fusion protein consisting of the N-terminal half of the AraC protein and the DNA-binding domain of the LexA repressor dimerizes, binds well to a LexA operator, and represses expression of a LexA operator-beta-galactosidase fusion gene in an arabinose-responsive manner. In vivo and in vitro experiments also showed that a fusion protein consisting of the C-terminal half of the AraC protein and the leucine zipper dimerization domain from the C/EBP transcriptional activator binds to araI and activates transcription from a PBAD promoter-beta-galactosidase fusion gene. Dimerization was necessary for occupancy and activation of the wild-type AraC binding site.
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PMID:Functional domains of the AraC protein. 851 13

A bacterial strain that was able to mineralize 2,4,6-trichlorophenol was isolated from a chlorophenol-fed percolator and was identified as a member of the genus Rhodococcus on the basis of chemotaxonomic characteristics and 16S RNA phylogenetic inference data. This organism (strain MBS1T [T = type strain]) exhibited a typical irregular rod-coccus cycle, and the cells had fimbria-like structures on their surfaces. The diagnostic cell wall amino acid was meso-diaminopimelic acid, and the sugars were arabinose and galactose; the mycolic acids contained 46 to 54 carbon atoms. The main menaquinone was MK-8(H2), and MK-9(H2) was a minor component. The cellular phospholipids were phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositolmannoside, phosphatidylglycerol, and diphosphatidylglycerol. Tuberculostearic acid was present. The whole-cell fatty acids were straight-chain acids with 14 to 18 C atoms. The G+C content of the DNA was 67.4 mol%. This organism grew on sucrose, pyruvate, and 2,4,6-trichlorophenol, and it oxidized a large number of carbon compounds, including catechol, 3-hydroxyphenylacetic acid, and phenol. It also exhibited beta-galactosidase, urease, and 2-acetyl-lactate decarboxylase activities. On a phylogenetic tree that was based on 16S ribosomal DNA gene sequences strain MBS1T was found among the rhodococci on an independent branch. On the basis of the chemotaxonomic and phenotypic characteristics of strain MBS1T and its phylogenetic position we suggest that this bacterium should be placed in a new species, Rhodococcus percolatus; the specific epithet was chosen because the organism was isolated by using an enriched percolator. The type strain is strain MBS1.
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PMID:Rhodococcus percolatus sp. nov., a bacterium degrading 2,4,6-trichlorophenol. 857

Thermotoga neapolitana is a hyperthermophilic bacterium whose phylogenetic lineage includes the most primitive of the bacterial heterotrophs. It is not known whether Thermotoga exhibits preferences for growth substrates or regulates the synthesis of degradative enzymes. We have found that T. neapolitana exhibits diauxic growth in medium containing 300 microM glucose and 1 mM lactose. We measured the activity of beta-galactosidase and beta-glucosidase in extracts prepared from cells grown on defined media and found that cells grown on 0.5% lactose, galactose or cellobiose contained beta-galactosidase specific activities of 1.19, 1.78 and 1.34 U (mg protein)-1, respectively. Cells grown on 0.5% glucose, maltose, fructose, sucrose, xylose, ribose or starch had no measurable beta-galactosidase activity. beta-Glucosidase activity was found only in cells grown on cellobiose. Cells grown on the combination of 0.5% lactose or galactose and 0.05% glucose had no detectable beta-galactosidase activity, whereas up to 0.5% glucose did not prevent expression of beta-galactosidase or beta-glucosidase activity in cells induced with 0.5% cellobiose. These activities are catalysed by separate enzymes as determined by resolution of their activities on 6% native polyacrylamide gels. Therefore, only beta-galactosidase synthesis induced by lactose is subject to catabolite repression. To determine the mechanism of catabolite repression, the levels of cAMP were measured in T. neapolitana cells grown on various defined media using an enzyme-immunoassay. The cAMP levels ranged from 44 to 280 fmol (mg protein)-1 irrespective of the carbon source used. By comparison, Escherichia coli grown on lactose contained 5.1 pmol (mg protein)-1. Like Gram-positive bacteria, T. neapolitana displays a cAMP-independent mechanism for catabolite repression and this may represent the more ancient mode of regulation.
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PMID:Catabolite repression in the hyperthermophilic bacterium Thermotoga neapolitana is independent of cAMP. 858 Nov 60

Aspergillus niger cinnamoyl esterase (CinnAE) is shown to be active towards a wide range of feruloylated oligosaccharides derived from sugar-beet pulp (SBP). The esterase hydrolysed ferulic acid ester-linked to either C-2 of arabinose or C-6 of galactose residues, and demonstrated the highest activity towards the feruloylated arabinose trisaccharide. However, CinnAE was able to release only 0.88% of total alkali-extractable ferulic acid from SBP in 24 h when acting alone. To determine whether cell-wall-degrading enzymes could increase the release of ferulic acid by CinnAE, SBP was incubated with various carbohydrases [cellulase, polygalacturonase, endo-arabinanase, alpha-L-arabinofuranosidase, endo-(1,4-beta-D-galactanase, beta-D-galactosidase]. These were added alone and in pairs, both in the presence and absence of CinnAE. We showed that all the carbohydrases tested were free of esterase activity. When individual carbohydrases were incubated with SBP, whether in the presence or absence of CinnAE, less than 1% of the feruloyl groups were released. When incubated with a mixture of endo-arabinanase and alpha-L-arabinofuranosidase, the esterase was able to release 14 times more of the alkali-extractable ferulic acid present in the whole pulp as free acid than CinnAE alone. Ferulic acid is linked either to L-arabinose or D-galactose in SBP, but no corresponding increase in ferulic acid release was detected when SBP was incubated with CinnAE plus endo-(1,4)-beta-D-galactanase and beta-D-galactosidase (both from A. niger). Hence feruloylated arabinans in SBP are readily available for hydrolysis by arabinan-degrading enzymes, whereas feruloylated galactans are not available for hydrolysis by galactan-degrading enzymes.
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PMID:Release of ferulic acid from sugar-beet pulp by using arabinanase, arabinofuranosidase and an esterase from Aspergillus niger. 867 11

Transcriptional regulation of the rhaT gene, one of the operons forming the rhamnose regulon in Escherichia coli, was studied by fusing its complete or deleted promoter to the reporter gene lacZ. Analysis of beta-galactosidase activities induced in these constructions grown under different conditions predicted the presence of two putative control elements: one for the RhaS regulatory protein and activating the gene not only by L-rhamnose but also by L-lyxose or L-mannose, the other for cAMP-catabolite repression protein and activating this gene in the absence of glucose. Anaerobiosis increased the promoter function two- to threefold with respect to the aerobic condition. Experiments involving complementation of strains containing the rhaT-promoter fusion and carrying a deletion in the rhaS and/or rhaR genes with plasmids bearing the rhamnose regulatory genes showed that rhaT is controlled by a regulatory cascade, in which RhaR induces rhaSR and the accumulated RhaS directly activates rhaT.
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PMID:Transcriptional regulation of the Escherichia coli rhaT gene. 875 46

We have isolated two phenotypically distinct nonfastidious Francisella strains (Fx1 and Fx2) from the blood of compromised patients with pneumonia and compared them with eight other Francisella strains, including Francisella tularensis biovar tularensis, F. tularensis biovar novicida, and F. philomiragia. Our isolates grew well on sheep blood agar, chocolate agar, modified Thayer-Martin agar, and Trypticase soy agar. Fx1 and Fx2 were determined to be within the Francisella genus by cellular fatty acid analysis and by the utilization of glucose, production of H2S and catalase, and lack of motility, oxidase, nitrate reductase, and gelatinase. They were additionally shown to belong to the species F. tularensis by sequencing of two variable regions comprising approximately 500 nucleotides of the 16S rRNA gene. Also, RNA probe hybridization confirmed their belonging to the species F. tularensis. However, the new strains, which are not identical, are distinguished from other F. tularensis strains by growth characteristics, repetitive extragenic palindromic PCR fragment pattern, and some biochemical tests. Key biochemical differences included the findings that Fx1 was positive for beta-galactosidase and arabinose hydrolysis and that both strains were citrulline ureidase positive and glycerol negative. Commercial F. tularensis antiserum agglutinated stock F. tularensis strains but not Fx1, Fx2, F. tularensis biovar novicida, or F. philomiragia; serum from either patient failed to agglutinate or only weakly agglutinated commercial antigen but showed agglutination when tested against each patient's respective isolate. Fx1 and Fx2 produced beta-lactamase. Because of their good growth, negative serology, and biochemical profile, the organisms could be misidentified in the clinical laboratory if standard strategies or commercial identification systems are used.
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PMID:Characterization of two unusual clinically significant Francisella strains. 881 97

Production of beta-galactosidase by Sclerotium rolfsii NCIM 1084 was studied under submerged fermentation conditions. The enzyme was produced extracellularly and constitutively on glucose. The enzyme production was enhanced when galactose, raffinose, cellobiose, sucrose, xylose, maltose, cellulose and pectin were used as carbon sources. Cellulose and diammonium hydrogen phosphate were best carbon and nitrogen sources, respectively. Surfactants such as Sag, Paraffin oil, Tween 20 and Tween 80 increased the enzyme production. Maximum yield of beta-galactosidase obtained was 3.8-4.2 nkat/ml. The optimum pH, optimum temperature and molecular weight of the beta-glactosidase were 2.7, 60 degrees C and 2,21,000 daltons, respectively. The enzyme is an aryl beta-glactosidase and did not hydrolyse lactose. The Km value for o-nitrophenyl beta-D-galactoside was 3.7 mM. Galactose and 2-mercaptoethanol inhibited the enzyme.
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PMID:Aryl beta-galactosidase from Sclerotium rolfsii: physiological and biochemical studies. 897 38


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