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)

Galactose mutarotase catalyzes the first step in normal galactose metabolism by catalyzing the conversion of beta-D-galactose to alpha-D-galactose. The structure of the enzyme from Lactococcus lactis was recently solved in this laboratory and shown to be topologically similar to domain 5 of beta-galactosidase. From this initial X-ray analysis, four amino acid residues were demonstrated to be intimately involved in sugar binding to the protein: His 96, His 170, Asp 243, and Glu 304. Here we present a combined X-ray crystallographic and kinetic analysis designed to examine the role of these residues in the reaction mechanism of the enzyme. For this investigation, the following site-directed mutant proteins were prepared: H96N, H170N, D243N, D243A, E304Q, and E304A. All of the structures of these proteins, complexed with either glucose or galactose, were solved to a nominal resolution of 1.95 A or better, and their kinetic parameters were measured against D-galactose, D-glucose, L-arabinose, or D-xylose. From these studies, it can be concluded that Glu 304 and His 170 are critical for catalysis and that His 96 and Asp 243 are important for proper substrate positioning within the active site. Specifically, Glu 304 serves as the active site base to initiate the reaction by removing the proton from the C-1 hydroxyl group of the sugar substrate and His 170 functions as the active site acid to protonate the C-5 ring oxygen.
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PMID:The catalytic mechanism of galactose mutarotase. 1271 27

The induction of the synthesis of secreted enzymes endo-1,4-beta-xylanase (EC 3.2.1.8) and beta-galactosidase (EC 3.2.1.23) in the original and recombinant Penicillium canescens strains has been studied. In all producer strains, the synthesis of these enzymes was induced by arabinose and its metabolite arabitol. The two enzymes differed in the concentration of arabinose required for the induction: the synthesis of beta-galactosidase was most pronounced at 1 mM, whereas maximum synthesis of endo-1,4-beta-xylanase was observed at 5 to 10 mM. An increase in the number of endo-1,4-beta-xylanase copies in the high-copy-number strain of the fungus suppressed the synthesis of beta-galactosidase; the synthesis of endo-1,4-beta-xylanase in the high-copy-number recombinant producing beta-galactosidase was affected to a lesser extent. The amount of the enzymes synthesized did not depend on the saccharide used as a sole source of carbon for growing the mycelium prior to its transfer to the inducer-containing medium.
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PMID:[Induction of endo-1,4-beta-xylanase and beta-galactosidase in the original and recombinant strains of the fungus Penicillium canescens]. 1272 49

The fungus Penicillium canescens strain F178 (VKPM) and its niaD- mutant exhibited an increased capability of synthesizing extracellular enzymes beta-galactosidase (70-80 U/ml) and xylanase (100 U/ml). The synthesis was induced by arabinose and its catabolite, arabitol. A deficiency in arabitol dehydrogenase, leading to arabitol accumulation in the cell, was detected in the chain of reactions of arabinose catabolism. The increased synthesis of beta-galactosidase and xylanase in P. canescens is accounted for by (1) cellular accumulation of the inducer (arabitol) at low concentrations of arabinose in the medium and (2) prevalence of induction over repression.
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PMID:[Mechanism of overproduction of secreted enzymes in the mycelial fungus Penicillium canescens]. 1275 25

The synthesis of isofagomine lactams (2-oxoisofagomines) corresponding to the biologically important hexoses is presented. The D-glucose/D-mannose analogue (3S,4R,5R)-3,4-dihydroxy-5-hydroxymethylpiperidin-2-one (9) was synthesised in 9 steps from D-arabinose, the D-galactose analogue (3S,4S,5R)-3,4-dihydroxy-5-hydroxymethylpiperidin-2-one (10) was synthesised in 11 steps from D-arabinose and the L-fucose analogue (3R,4R,5R)-3,4-dihydroxy-5-methylpiperidin-2-one (11) was synthesised in 12 steps from L-arabinose. The three lactams 9-11 were found to be glycosidase inhibitors with micro- to nanomolar inhibition constants. The lactam 10 showed slow onset inhibition of beta-galactosidase from A. Oryzae. The rate constants for this process were determined to be k(on) = 2.55 x 10(4) M-1 s-1 and k(off) = 1.7 x 10(-3) s-1. The activation energies and standard thermodynamic functions were also determined.
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PMID:Isofagomine lactams, synthesis and enzyme inhibition. 1292 23

1. An experimental system suitable for the study of enzyme formation has been described. 2. The formation of beta-galastosidase in E. coli B could be induced by lactose, melibiose, D-galactose and beta-methyl-D-galactoside. 3. Lactose-induced beta-galactosidase formation was found to be inhibited by D-glucose, D-mannose, D-fructose, D-arabinose, and raffinose. 4. The utilizable structural analogue, D-glucose, was found to either stimulate or inhibit beta-galactosidase formation depending upon its concentration. D-Arabinose, on the other hand, a non-utilizable structural analogue, is only capable of inhibiting, whereas succinic acid, a structurally unrelated energy source, is only capable of stimulating beta-galactosidase formation. 5. D-Arabinose inhibition of lactose-induced beta-galactosidase formation was found to be of the competitive type. 6. Some of the implications of these findings have been discussed.
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PMID:The mechanism of the synthesis of enzymes. I. Development of a system suitable for studying this phenomenon. 1305 5

Escherichia coli B synthesized beta-galactosidase and an enzyme system for D-xylose when exposed to lactose and xylose respectively in nitrogen-free media. The amount of beta-galactosidase formed in the absence of external nitrogen depended upon the nature of the medium in which the cells had originally been grown. Half as much of this enzyme was synthesized without exogenous nitrogen by cells taken from a nitrogen-rich medium as was formed by cells under favorable conditions with an external supply of nitrogen. Escherichia coli B contained a pool of nitrogen compounds soluble in 80 per cent ethanol and made up of several ninhydrin-positive components. One of these was identified chromatographically as glycine using an authentic radioactive sample. Another substance behaved like serine on the chromatograms. The internal pool of amino acids and peptides was large enough to account for the beta-galactosidase synthesized by cells exposed to lactose in a medium free of nitrogen. Some degree of interaction of the syntheses of the beta-galactosidase and xylose enzyme systems was observed in nitrogen-free media. This interaction produced a greater effect on the formation of beta-galactosidase and was attributed to a limiting factor(s) in the internal nitrogenous pool or to a limiting intermediate in enzyme synthesis.
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PMID:Enzyme biosynthesis in Escherichia coli. 1366 21

Johnson, E. M. (Walter Reed Army Institute of Research, Washington, D.C.), Stanley Falkow, and L. S. Baron. Recipient ability of Salmonella typhosa in genetic crosses with Escherichia coli. J. Bacteriol. 87:54-60. 1964.-Salmonella typhosa strain 643WS(r) was mated with Escherichia coli Hfr strains W1895 and Hayes, with single marker selection for the E. coli genes lac(+) (lactose utilization) and ara(+) (arabinose utilization). Four classes of Salmonella hybrids were obtained, each class possessing one marker derived from one E. coli parent. In a series of eight genetic crosses, in which each hybrid class was remated with each of the Hfr strains, recipient ability of the hybrids was increased only when their substituted E. coli genetic section matched the lead region of the Hfr chromosome. Data obtained from replica plating indicated that the S. typhosa 643WS(r) population is probably homogeneous with respect to its initial ability to mate with E. coli. Transfer of the F-lac element was found to occur only slightly less efficiently from an E. coli F' donor to S. typhosa than it did to an E. coli F(-) strain. This indicated that E. coli is able to conjugate almost as effectively with S. typhosa as it does intraspecifically. However, failure to detect beta-galactosidase production by merozygotes derived from an E. coli Hfr W1895 x S. typhosa mating indicated that transfer of chromosomal lac(+) may be impaired.
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PMID:RECIPIENT ABILITY OF SALMONELLA TYPHOSA IN GENETIC CROSSES WITH ESCHERICHIA COLI. 1410 74

Using methyl-1-thio-beta-D-galactoside as the inducer, the biosynthesis of beta-galactosidase was observed in Escherichia coli B with only endogenous sources of nitrogen and energy available. The addition of glucose, ribose, xylose, or glycerol as exogenous energy sources to nitrogen-deficient media blocked enzyme formation. Preinduction of the resting cells failed to overcome inhibition by the added energy sources. With limited quantities of glucose, ribose, xylose, or glycerol, synthesis of beta-galactosidase resumed abruptly and continued at the rate normal for cells in nitrogen-deficient media. Comparison of enzyme activities with oxygen uptake data revealed a reduction in the rate of oxygen uptake at the time enzyme synthesis resumed in media originally containing small amounts of energy sources. This change corresponded to only a fraction of the oxygen required for complete oxidation of one of the exogenous substrates. It is suggested that inhibition by these particular exogenous substrates involves metabolism to a common repressor or interference with an energy-transfer system.
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PMID:The effect of exogenous energy sources on the synthesis of beta-galactosidase in resting-cell suspensions of Escherichia coli. 1448 8

The ability to convert D-galactose into D-tagatose was compared among a number of bacterial L-arabinose isomerases ( araA). One of the most efficient enzymes, from the anaerobic thermophilic bacterium Thermoanaerobacter mathranii, was produced heterologously in Escherichia coli and characterised. Amino acid sequence comparisons indicated that this enzyme is only distantly related to the group of previously known araA sequences in which the sequence similarity is evident. The substrate specificity and the Michaelis-Menten constants of the enzyme determined with L-arabinose, D-galactose and D-fucose also indicated that this enzyme is an unusual, versatile L-arabinose isomerase which is able to isomerise structurally related sugars. The enzyme was immobilised and used for production of D-tagatose at 65 degrees C. Starting from a 30% solution of D-galactose, the yield of D-tagatose was 42% and no sugars other than D-tagatose and D-galactose were detected. Direct conversion of lactose to D-tagatose in a single reactor was demonstrated using a thermostable beta-galactosidase together with the thermostable L-arabinose isomerase. The two enzymes were also successfully combined with a commercially available glucose isomerase for conversion of lactose into a sweetening mixture comprising lactose, glucose, galactose, fructose and tagatose.
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PMID:Enzymatic conversion of D-galactose to D-tagatose: heterologous expression and characterisation of a thermostable L-arabinose isomerase from Thermoanaerobacter mathranii. 1516 95

The allosteric mechanism by which the gene expression regulatory protein AraC regulates its DNA-binding activity is shown to be portable by grafting it to beta-galactosidase, generating an arabinose-regulated beta-galactosidase. A portion of the alpha-peptide sequence that complements the activity of alpha-acceptor beta-galactosidase was inserted into a nonessential region of the regulatory peptidyl arm of AraC protein. Arabinose, which regulates the position of the arm in AraC protein now regulates the availability of the alpha-peptide to alpha-acceptor beta-galactosidase, thereby modulating its activity in response to arabinose.
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PMID:A portable allosteric mechanism. 1532 89


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