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)

Six hybridomas producing monoclonal antibodies against Escherichia coli beta-galactosidase (beta-D-galactoside galoctohydrolase, EC 3.2.1.23) have been derived from two separate somatic cell fusions. Three of these antibodies can activate defective enzymes produced by strains of E. coli carrying Z-gene point mutations. In antigen excess, one monoclonal antibody shows similar enzyme binding and mutant-activating capacity. Characteristically, the former reaction has a 200-fold higher equilibrium constant. These data provide direct evidence that the enzyme-activation reaction is a single-hit event in which one antibody site favors the correct conformation of one active center of the enzyme. Because each "activating" hybridoma is able to activate several but not all point mutant enzymes tested, it appears that the correction of the genetic defect is produced by binding key sites of the protein three-dimensional structure rather than the sites affected by the mutation.
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PMID:Antibody-mediated activation of genetically defective Escherichia coli beta-galactosidases by monoclonal antibodies produced by somatic cell hybrids. 678 6

Oxygen-18 leaving group kinetic isotope effects (KIEs) have been determined on both Vmax (V) and Vmax/Km (V/K) for the beta-galactosidase-catalyzed hydrolysis of p-nitrophenyl beta-D-galactoside (I) and 2,4-dinitrophenyl beta-D-galactoside (II). The former substrate exhibits KIEs of 1.022 +/- 0.002 and 1.014 +/- 0.003 on V and V/K, respectively, while corresponding KIEs for the latter are 1.002 +/- 0.0009 and 1.030 +/- 0.003. These results indicate that bond scission is largely rate determining for I but not for II at substrate saturation. The first irreversible step for both substrates must involve cleavage of the bond to the nitrophenyl leaving group. The mechanism proposed for this reaction is characterized by two parallel pathways for substrate hydrolysis. The predominant route for all but the most reactive substrates involves a SN2 nucleophilic displacement of aglycon by the enzyme to yield a covalent galactosyl-enzyme which in turn is hydrolyzed via a nucleophilic attach by water. The most reactive substrates (e.g., II) from transiently an enzyme-bound galactosyl oxo-carbonium ion which partitions between enzyme to give the covalent galactosyl-enzyme and H2O to yield galactose.
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PMID:Oxygen-18 leaving group kinetic isotope effects on the hydrolysis of nitrophenyl glycosides. 1. beta-galactosidease-catalyzed hydrolysis. 678 82

Acid beta-D-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) was purified to near homogeneity from normal human urine by two affinity chromatography steps. On polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate the major protein band had an apparent molecular weight of 59000, thus being 5000 daltons smaller than the protein purified from human liver. Upon gel filtration on Sephadex G-150 column the purified enzyme had an apparent molecular weight of 70000 of pH 7.0. At pH 4.0 partial aggregation to a dimer of an apparent molecular weight of 150000 was found. Addition of 0.1 M galactose caused at pH 3.5, but not at pH 4.0 and 7.0, an increased formation of multimeric beta-galactosidase which eluted with the void volume of the column. Crude beta-galactosidase from human urine showed a higher aggregation tendency than the purified enzyme. None of the conditions produced an enzyme species of an apparent molecular weight of less than 40000. pH-activity profiles were measured against p-nitrophenyl-beta-D-galactoside, 3H-labelled GM1-ganglioside, [3H]keratan sulfate and the pentasaccharide O-beta-(1 leads to 4)-[6-3H]galactopyranosyl-O-beta-(1 leads to 2)-2-deoxy-2-acetamidoglycopyranosyl-O-alpha-(1 leads to 6)-mannopyranosyl-O-beta-(1 leads to 4)-mannopyranosyl-2-deoxy-2-acetamidoglucopyranoside. While p-nitrophenyl-beta-D-galactopyranoside and GM1-ganglioside were optimally hydrolyzed at pH 4.0, keratan sulfate and the pentasaccharide were optimally degraded at pH 4.3 and pH 5.0, respectively. With the chromogenic substrate and with GM1-ganglioside Km values of 0.33 mM were calculated. At pH 3.5 the hydrolysis of the synthetic substrate did not follow Michaelis-Menten kinetics. Two enzyme species appeared with Km values of 0.006 mM and 3.2 mM, respectively. The affinity of beta-galactosidase for [3H]keratan sulfate and the 3H-labelled pentasaccharide was at least one order of magnitude lower than for the amphiphilic substrates. Keratan sulfate and GM1-ganglioside did not act as competitive inhibitors of p-nitrophenyl-beta-galactosidase at the concentration tested. These findings could be explained by the existence of different binding sites for the substrates used.
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PMID:Aggregation properties of beta-galactosidase of human urine and degradation of its natural substrates by a purified preparation of the enzyme. 680 47

1) Two forms of acid beta-galactosidase [EC 3.1.23] with different molecular weights catalyzing the hydrolysis of GM1-ganglioside and p-nitrophenyl-beta-D-galactoside were separated and purified from porcine spleen. 2) The apparent molecular weights were 400,000-600,000 and 70,000-74,000 for the high (termed Am form) and low (termed A1 form) molecular weight forms, respectively. 3) On examination by sodium dodecyl sulfate (SDS)/polyacrylamide gel electrophoresis, both forms of the enzyme had a common protein band of molecular weight 63,000, and the Am form showed three additional protein bands with molecular weights of 31,000, 21,000, and 20,000. 4) Both forms of the enzyme had similar catalytic functions with regard to pH-optimum, Km, substrate specificity and sensitivity to substrate analogues and other substances such as detergents, bovine serum albumin (BSA) and NaCl. 5) Both forms of the enzyme were fairly stable upon preincubation at 45 degrees C at acidic pH (pH 4.5), but lost their activities at neutral pH (pH 7.0). 6) The A1 form was a monomer at neutral pH (pH 7.0) and formed a dimer at acidic pH (pH 4.5). However, most of the Am form could not be converted to a dimeric form on gel filtration at acidic pH.
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PMID:The interrelation between high- and low-molecular-weight forms of GM1-beta-galactosidase purified from porcine spleen. 681 70

1. A method is described for following continuously the action of beta-galactosidase on 4-methylumbelliferyl beta-D-galactoside at pH 4.5, in which 4-methylumbelliferone production is measured at fluorescence excitation and emission wavelengths of 324 and 444nm respectively. 2. Initial-rate studies show that the presence of salt activates beta-galactosidase up to 100 mM, but is inhibitory above that concentration. The enzyme is very unstable at 37 degrees C and low ionic strength, but stability increases with ionic strength. 3. The stability of the enzyme at 37 degrees C decreases markedly with rising pH in the range 5.9--8.0. 4. Gel-filtration patterns demonstrate that there is a marked tendency to polymerization with increasing ionic strength. The gel-filtration pattern shows decreasing amounts of dimer with increasing pH. 5. The correlation between activity, stability and molecular form of beta-galactosidase is discussed. It is suggested that the dimeric form of the enzyme is the most stable and active form. The implications of this finding for the assay of beta-galactosidase under physiological conditions for prenatal diagnosis are discussed. 6. Evidence for the possible occurrence of a 36 000-mol.wt. from of beta-galactosidase is presented. 7. A computer program for the calculation of initial rates has been deposited as Supplementary Publication SUP 50114 (4 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1981) 193, 5.
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PMID:The stability and aggregation properties of human liver acid beta-D-galactosidase. 730 60

The present study describes a novel method for the histochemical demonstration of beta-galactosidase activity on tissue sections. We have replaced 5-bromo-4-chloro-3-indolyl-beta-D-galactoside (X-Gal) with 5-bromo-indolyl-beta-o-galactopyranoside (Bluo-Gal) as a chromogenic substrate for the bacterial beta-galactosidase (lacZ). After beta-galactosidic cleavage, Bluo-Gal precipitates in form of fine birefringent crystals, whereas X-gal gives rise to an amorphous precipitate. Upon microscopic examination under polarized light, the crystals emit a strong signal consisting of yellow reflected light. This property of Bluo-Gal results in greatly enhanced sensitivity of the staining method for beta-galactosidase and allows for optimal morphological resolution. To exemplify the applications of this technique, the expression is demonstrated in transgenic mice of beta-galactosidase driven by a fragment of the human tissue-type plasminogen activator promoter.
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PMID:Improved in situ beta-galactosidase staining for histological analysis of transgenic mice. 753 99

We have developed a eukaryotic expression vector that provides a rapid and sensitive measure of transcriptional activity modulated by general and tissue-specific regulatory motifs. The lacZ structural gene has been linked to the minimal promoter of the human liver/bone/kidney alkaline phosphatase gene. In addition, a trimerized cassette of the SV40 polyadenylation region has been placed 5' of this promoter to reduce plasmid-initiated transcripts extending through the lacZ gene that would contribute to background beta-galactosidase (beta-Gal) activity. By combining the weak promoter and the poly(A) cassette, only a very low level of lacZ activity is detected in the absence of additional regulatory sequences. Regulatory domains can be inserted into this vector via a unique Bam HI restriction site and their activity can be rapidly monitored in situ via a colorimetric 5-bromo-4-chloro-3-indolyl-beta-D-galactoside (X-Ga) staining protocol. Also, the activity of linked regulatory domains can be measured quantitatively by assaying beta-Gal levels in cell extracts. We show that derivatives of this vector can be used to monitor the activity of general and tissue-specific control elements and can be transactivated by a single transcription factor in cotransfection experiments.
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PMID:A sensitive lacZ-based expression vector for analyzing transcriptional control elements in eukaryotic cells. 762 23

The lacZY gene cassette inserted into the chromosome of Pseudomonas aeruginosa UG2Lr and Pseudomonas aureofaciens Ps3732RNL11 was used as a genetic marker to study the fate of the Pseudomonas strains in river water microcosms. Expression of the lacZ marker in UG2Lr and Ps3732RNL11 was detected in microcosms containing as few as 12 and 14 colony-forming units (cfu)/mL of river water, respectively, by fluorimetric measurement of the beta-galactosidase activity against 4-methylumbelliferyl-beta-D-galactoside as the substrate. The persistence of and lacZ expression in the pseudomonas strains were monitored in sterile and nonsterile river water in the presence and absence of added nutrients by dilution plating and fluorimetry, respectively. After incubation for 10 d at 10 degrees C, culturable populations of strain UG2Lr in sterile water samples, with and without nutrient added, decreased from an initial density of 1.5 x 10(4) to 1.7 x 10(3) and 4.6 x 10(3) cfu/mL, respectively. Despite similar numbers of UG2Lr cells in the two treatments, expression of the lacZ marker in the surviving cells of the nutrient-supplemented sample was 24 times higher than in the cells of the unamended sample. In nonsterile water samples, the density of UG2Lr declined to less than 6 cfu/mL in 30 d regardless of the nutrient conditions. A nutrient supplement increased the growth of the native bacterial population but did not enhance growth of and lacZ expression in the bacteria. Polymerase chain reaction analysis showed a decrease in amplification signal indicating a genuine decline in viable UG2Lr cell density in the water samples.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Survival of and lacZ expression in recombinant Pseudomonas strains introduced into river water microcosms. 762 6

A new medium containing 5-bromo-4-chloro-3-indolyl-beta-D-glucuronide cyclohexylammonium salt (Glu agar) for Escherichia coli and a new medium containing 5-bromo-3-indolyl-beta-D-galactoside (Gal agar) for beta-galactosidase-positive members of the family Enterobacteriaceae were compared with MacConkey agar in a diagnostic trial with 3,562 urine specimens. The isolation rates of E. coli and beta-galactosidase-positive Enterobacteriaceae were increased 8.4 and 19.5%, respectively. The sensitivities and specificities of Glu agar and Gal agar were 98.5 and 100% and 99.2 and 99.5%, respectively.
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PMID:Evaluation of new medium with chromogenic substrates for members of the family Enterobacteriaceae in urine samples. 769 41

We have characterized a new psychrotrophic Arthrobacter isolate which produces beta-galactosidase isozymes. When DNA from this isolate was transformed into an Escherichia coli host, we obtained three different fragments, designated 12, 14, and 15, each encoding a different beta-galactosidase isozyme. The beta-galactosidase produced from fragment 12 was of special interest because the protein subunit was smaller (about 71 versus 116 kDa) than those typically encoded by the lacZ family. The isozyme encoded by fragment 12 was purified, and its activity and thermostability were examined. Although the enzyme is highly specific towards beta-D-galactoside substrates, its levels in the isolate do not increase in cells grown with lactose. Nucleotide sequence determination showed that the gene encoding isozyme 12 is not similar to the other members of the lacZ family but has regions similar to beta-galactosidase isozymes from Bacillus stearothermophilus and B. circulans. Addition of the isozyme 12 sequence to the database made it possible to examine these enzymes as possible members of a new, separate family. Our analysis of this new family showed some conserved amino acids corresponding to the lacZ acid-base catalytic region but no homology with the nucleophilic region. On the basis of these comparisons, we designated this a new lacG family.
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PMID:Analysis of a novel gene and beta-galactosidase isozyme from a psychrotrophic Arthrobacter isolate. 772 89


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