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)

1. The dependence of the rate of accumulation of methyl-alpha-D-glucoside on its extracellular concentration was studied in the tgl mutant of Escherichia coli K12, isolated earlier. It has been shown that the kinetics of methyl-alpha-D-glucoside transport differ sharply from those in wild-type bacteria. 2. The beta-galactosidase synthesis in tgl strain is much less sensitive both to permanent and transient glucose catabolite repression. The level of cyclic AMP in mutant cells under the conditions of glucose catabolite repression is several times higher than in the parent strain. 3. The tgl mutation does not affect the manifestation of catabolite inhibition and inducer exclusion with glucose. 4. The data obtained are discussed in the light of a hypothesis concerning the existence of two sites, binding and pecific enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system. The tgl mutation alters the first site, and the second one is damaged by the pgt mutation. 5. It is suggested that the products of the tgl and gpt genes are necessary for the manifestation of the phenomena of glucose permanent and transient repression. The effects of catabolite inhibition and inducer exclusion are realized irrespective of the existence or absence of the tgl product.
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PMID:Glucose effect in tgl mutant of Escherichia col K12 defective in methyl-alpha-D-glucoside transport. 18 55

The uptake of 4-deoxy-4-fluoro-D-glucose (4FG), without subsequent catabolism, by resting cells of Escherichia coli (ATCC 11775) is 0.06 mg/mg dry weight. In frozen-thawed cells of this organism, 4FG is a substrate for the phosphoenolpyruvate phosphotransferase system with a rate of phosphorylation twice that found for the isomeric 3-deoxy-3-fluoro-D-glucose. 4FG is not a carbon source for growth of this organism and it inhibits the extent of growth of cells in the presence of glucose. The inhibition of growth of E. coli K12 on lactose by 4FG is also observed and this is considered to be consistent with the fact that 4FG is an uncompetitive inhibitor of beta-galactosidase (EC 3.2.1.23) activity and that 4FG or 4-deoxy-4-fluoro-D-glucose-6 phosphate repress beta-galactosidase synthesis. These results support the view that catabolite repression may be produced by compounds which are not necessarily metabolised further than hexose-6-phosphates.
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PMID:Some biochemical effects of 4-deoxy-4-fluoro-D-glucose on Escherichia coli. 19 27

The effects of glucose and glucose-6-phosphate in initiating the repression of beta-galactosidase synthesis were studied using a mutant of Escherichia coli K12 which lacks glucose-specific enzyme II of the phosphoenolpyruvate-sugar phosphotransferase system. It was found that glucose-6-phosphate causes transient repression of beta-galactosidase synthesis but glucose does not cause transient repression in this mutant. Evidence was obtained that both the presence of an active transport system for glucose-6-phosphate in the cells and glucose-6-phosphate in the medium are necessary for the initiation of transient repression. No metabolism of glucose-6-phosphate is required. Upon depletion of glucose-6-phosphate in the medium the transient repression was reversed. After the reversal the rate of enzyme synthesis was high in the cells which had been exposed to a high concentration of glucose-6-phosphate. It was concluded that the translocation of glucose-6-phosphate across the membranes is the primary event which affects both the initiation of and the recovery from the transient repression. During the transient repression the cellular content of cyclic adenosine 3',5'-monophosphate decreased significantly.
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PMID:Transient repression of beta-galactosidase synthesis by glucose-6-phosphate in a mutant of Escherichia coli lacking enzyme II specific for glucose in the phosphoenolpyruvate-sugar phosphotransferase system. 20 84

The subcellular localization of aminopeptidase N (previously called aminoendopeptidase) has been investigated. This enzyme was found to be partially released (30-40%) by osmotic shock or by converting Escherichia coli K10 cells to spheroplasts. However, in all other E. coli strains (K12, B/r, MRE 600, ML 308) tested, this enzyme is not released at all by these procedures and thus behaves like a cytoplasmic enzyme. The crypticity of aminopeptidase N is surprisingly low, 75-85% of the enzyme activity is directly assayable in intact cells of any E. coli strain. Various inhibitors of transport systems do not interfer with this assay. Aminopeptidase activity could also be assayed in spheroplasts, even when an insolubilized substrate was used, which suggests a surface location of this enzyme. As well, N-ethylmaleimide (0.4 mM), under conditions which do not allow penetration in the cytoplasm, caused 70% inhibition of aminopeptidase N. Binding of 125I-labeled antiaminopeptidase N antibody to spheroplasts (from K12 strain) was used to assay the orientation of aminopeptidase N in the membrane. This enzyme is exposed on the outer surface of the cytoplasmic membrane. Confirmation of this orientation was obtained by comparing the accessibility of aminopeptidase, alkaline phosphatase and beta-galactosidase to fluorescamine in intact cells. Only 16% of the total beta-galactosidase was labeled with this fluorescent reagent whereas 44-45% of the aminopeptidase N and 59% of the alkaline phosphatase were labeled. Electron microscopic visualization of insolubilized reaction products of aminopeptidase N within the cells showed that these products are located at the poles of the cells. Neither mutant cells which were devoid of aminopeptidase N activity nor parental strains with the enzyme activity inhibited with phenylmercuric chloride contained the characteristic black caps. Thus, it appears that the periplasm is enlarged at the poles of the cells and that the reaction product is mainly located in these places. Investigation of the type of interactions of aminopeptidase N with the plasma membrane only revealed that aminopeptidase N has mainly an electrostatic interaction with the outer surface, probably mediated by magnesium ion bridges. Additional interactions are involved since disruption of the integrity of the cytoplasmic membrane is required to totally release this enzyme.
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PMID:Aminopeptidase N from Escherichia coli. Unusual interactions with the cell surface. 32 10

The effect of structural modification on the enzyme-binding capacity of collagen has been studied using beta-galactosidase (E. coli K12) immobilized to collagen membrane by the impregnation procedure. The apparent steady-state activities of the resultant collagen-enzyme complexes were determined as a means of evaluating the enzyme-binding capacity of the modified collagen. In addition, the amount of enzymic protein bound to the collagen support was determined by the tryptophan content of the complex. The tertiary structure of the collage matrix was modified by cross-linking with the difunctional reagent, glutaraldehyde, and by aging in the dry state. Such structural modifications were found to markedly reduce the enzyme (beta-galactosidase) binding capacity of collagen films. The enzyme-binding capacity of the crosslinked collagen membrane was completely restored by proteolytic enzyme treatment of the aged film but only partly so for the glutaraldehyde treated films. Proteolytic enzymes used to treat a dispersion of collagen microfibrils prior to casting into a membrane also resulted in an increase in enzyme-binding. The effect of structural modification of collagen on enzyme-binding and the locus of enzyme attachment are discussed.
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PMID:Chemical modificiation of collagen and the effects on enzyme-binding: mechanistic considerations. 41 51

BETA-Galactosidase (EC 3.2.1.23), prepared from strains ML 308 and K12 3300 of Escherichia coli, dissociated into an inactive monomer in the presence of Ag+. When such a monomer preparation is treated with excess of thiol an enzymically active dimer is formed in addition to an active tetramer. It is suggested that Ag+ may be of value in studies on other multimeric proteins as a mild dissociating agent.
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PMID:Evidence for an active dimer of Escherichia coli beta-galactosidase. 76 50

Phi80dargECBH DNA has been used to direct cell-free synthesis of argininosuccinase, the argH gene product in Escherichia coli K12. In vitro enzyme synthesis is sensitive to repression by partially purified preparations from an argR+ strain but not by corresponding preparations from an argR- strain. Using DNA-cellulose chromatography, approximately seventyfold purification of repressor has been obtained. The partially purified preparation represses argininosuccinase synthesis but has no effect on beta-galactosidase synthesis.
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PMID:In vitro synthesis and repression of argininosuccinase in Escherichia coli K12; partial purification of the arginine repressor. 77 11

1. Two spontaneous Escherichia coli K12 mutants resistant to glucose catabolite repression were isolated using minimal agar plates with methyl alpha-D-glucoside. Mutants grow well on glucose and mannitol. 2. Glucose does not inhibit the inducible enzyme synthesis in isolated mutants: mutant cell (in contrast to parent cells) produce high levels of beta-galactosidase and L-tryptophanase under the conditions of glucose catabolite repression. 3. The isolated mutants are negative in methyl-alpha-D-glucoside transport; glucose uptake is not severely damaged. But the mutants (named tgl, transport of glucose) retained the ability to phosphorylate methyl alpha-D-glucoside in vitro at the expense of phosphoenolpyruvate. 4. The tgl mutation is cotransduced with purB and pyrC markers, i.e. locates near 24 min of the E. coli chromosome map. 5. It is thought that E. coli cells possess two glucose transport systems. The first one is represented by the glucose-specific enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system. The second glucose transport system (coded for tgl gene) functions as permease and possesses high affinity to methyl alpha-D-glucoside. The integrity of glucose permease determine the sensitivity of the cell to glucose catabolite repression.
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PMID:Glucose catabolite repression in Escherichia coli K12 mutants defective in methyl-alpha-d-glucoside transport. 109 69

The phenomenon of glucose catabolite repression was studied in Escherichia coli mutants unable to transport this carbohydrate. The pts I,H mutant P34 was much less sensitive to permanent and transient repressive effect of glucose on beta-galactosidase synthesis than parental type. The 1103 mutant with lack of enzyme 1 of the phosphoenolpyruvate-dependent phosphotransferase system (ptsI) behaves as well as P34 mutant after addition of glucose to casamino acids mineral medium. But in minimal medium with succinate as the sole source of carbon cells of the 1103 mutant (in accordance with the data of Perlman and Pastan, 1969) show hightened sensibility to transient glucose repression. The effect of hypersensibility disappears when the lacI mutation rendering the beta-galactosidase synthesis to costitutivity is introduced in 1103 mutant. It is shown that the hightened sensibility of beta-galactosidase synthesis to glucose transient repression in 1103 mutant is not an effect of the pts mutation and most probably is due to "inducer exclusion" of the lac operon. It is also shown that if one introduces the P34 mutation in strain devoided of one of the enzymes II for glucose (gptA) (and due to this resistant to glucose catabolite repression) then the level of resistance in double mutant does not increase in spite of considerable supression of 14C glucose accumulation. It is discussed the role of separate components of Escherichia coli K12 glucose transport system in realization of the phenomenon of catabolite repression.
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PMID:Catabolite repression in Escherichia coli K12 mutants defective in glucose transport. 110 54

bglY mutants of Escherichia coli K12 which show higher levels of kanamycin resistance (Kmr) in the presence of plasmid pGR71 have been previously described. In this work, we show that this increased resistance to an aminoglycoside antibiotic is not due either to low drug uptake or to alteration of its target, the ribosome. The copy number of plasmid pGR71 is not modified. The fact that increased antibiotic resistance is observed with only some of the Kmr determinants used in this study suggests a specific role for the bglY gene product. Moreover, for one such determinant, a higher level of resistance was observed when it was inserted in the chromosome but not when harbored by a plasmid. This discrepancy can be explained by the twin transcriptional-loop model, which proposes that transcription can lead to local variation in topology. A kan-lacZ fusion was constructed from the Kmr gene of plasmid pGR71 and inserted into a low copy number vector. Assay of beta-galactosidase in wild-type and mutant strains showed that expression of the antibiotic resistance gene was directly affected by H1 protein, the bglY gene product.
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PMID:Mutations in bglY, the structural gene for the DNA-binding protein H1 of Escherichia coli, increase the expression of the kanamycin resistance gene carried by plasmid pGR71. 131 98


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