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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 p-nitrophenyl beta-D-galactosidase asctivity in rat liver homogenates of lysosome-rich fractions was shown to be markedly affected by the ionic composition of the medium. A stimulation of the reaction rate at pH 5 was produced by most of the salts tested, which contained anions such as acetate, SO4(2-) and Cl-, and cations such as Na+, K= and Mg2+. The most pronounced effect was observed with MgCl2. Only potassium glutamate was inhibitory. 2. Five peaks of beta-galactosidase activity obtained by DEAE-cellulose chromatography were equally sensitive to changes in the ionic composition of the medium. In the presence of added NaC1, the whole rate-pH curve was displaced towards higher pH values, the optimum being shifted from 2.0-2.5 to 3.5. The stimulation at pH 5.0 appeared to be mainly due to changes in Vmax., whereas the apparent Km was slightly modified. 3. Unlike the total, the free beta-galactosidase activity remained unchanged or even declined when KC1 was added to the reaction medium.
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PMID:Stimulation of rat liver beta-galactosidase activity by ions. 0 74

A study was implemented to quantitate the hydrolase and transgalactosylase activities of beta-galactosidase (E. coli) with lactose as the substrate and to investigate various factors which affect these activities. At low lactose concentrations the rate of galactose production was equal to the rate of glucose production. The rate of galactose production relative to glucose, however, dropped dramatically at lactose concentrations higher than 0.05 M and production of trisaccharides and tetrasaccharides began (galactose/glucose ratios of about 2:1 and 3:1, respectively, were found for these two types of oligosaccharides). At least five different trissacharides were formed and their patterns of formation showed that they probably utilized both lactose and allolactose as galactosyl acceptors. Allolactose was produced in amounts proportional to glucose at all lactose concentrations (ratios of allolactose/glucose were about 0.88). Analyses of various data, including a reaction analyzed at very early times, showed that the major means of production of allolactose (and the only means initially) was the direct enzymatic transfer of galactose from the 4 position to the 6 position of the glucose moiety of lactose without prior release of glucose from the enzyme. It was shown, however, that allolactose could also be formed in significant quantities by the transfer of galactose to the 6 position of free glucose, and also by hydrolysis of preformed trisaccharide. A mechanism which fits the initial velocity data was proposed in which the steps involving the formation of an enzyme-gallactose-glucose complex, the formation and breakage of allolactose on the enzyme, and the release of glucose all seem to be of roughly equal magnitude and rate determining. Various factors affected the amounts of transgalactosylase and hydrolase activities occurring. At high pH values (greater than 7.8) the transgalactosylase/hydrolyase activity ratio increased dramatically while it decreased at low pH values (less than 6.0). At mid pH values the ratio was essentially constant. The absence of Mg2+ caused a large decrease in the transgalactosylase/hydrolase activity ratio while the absence of all but traces of Na+ or K+ had no effect. The anomeric configuration of lactose altered the transgalactosylase/hydrolase activity ratios, alpha-Lactose resulted in a decrease of allolactose production (transgalactosylase activity) relative to hydrolase activities (glucose production) while beta-lactose had the opposite effect.
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PMID:A quantitation of the factors which affect the hydrolase and transgalactosylase activities of beta-galactosidase (E. coli) on lactose. 0 22

The optimal reaction conditions and kinetic properties of eleven leukocyte acid hydrolases determined with the use of fluorigenic derivatives of 4-methyl-umbelliferone are described. The enzymes studied were acid phosphatase, aryl sulfatase, alpha- and beta-glucosidase, alpha- and beta-galactosidase, alpha-mannosidase, N-acetyl-beta-glucosaminidase, N-acetyl-beta-galactosaminidase, beta-glucuronidase and alpha-fucosidase. More than 90% of the activity of each enzyme was released into a 27,000 X g supernatant by a double sonication procedure employing 0.9% sodium chloride and 0.1% Triton X-100. The Km values obtained were similar to those previously reported for chromogenic subtrates. A single Km value could not be derived for beta-galactosidase because its double reciprocal plot was not linear. All enzymes could be measured with less than 10 mug of protein within 15 min. Activators and inhibitors studied included the chloride salts of Na+, K+, Zn2+, Ca2+, Mg2+, Hg2+, and Fe2+ as well as p-chloromercuriphenysulfonate, glutathione, BAL, EDTA, EGTA, Triton X-100 and sodium taurocholate. The reaction conditions described in this report can be used for the diagnosis of various lysosomal storage diseases and should facilitate the development of automated procedures for the analysis of these eleven enzyme activities with small quantities of blood.
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PMID:Human leukocyte acid hydrolases: characterization of eleven lysosomal enzymes and study of reaction conditions for their automated analysis. 0 26

Three beta-N-acetylhexosaminidases [EC 3.2.1.52] and one beta-galactosidase [EC 3.2.1.23] were purified from the culture filtrate of streptococcus 6646 group K by a combination of column chromatographies on p-aminophenyl beta-D-thiogalactopyranoside-substituted Sepharose and N-(paminophenyl)oxamic acid-substituted Sepharose. These beta-N-acetylhexosaminidases showed optimal activities between pH 5.0 and 5.5 and could hydrolyze synthetic and glycopeptidic substrates. Glycolipids such as GM2, asialo-GM2, and globoside I were no susceptible to these beta-hexosaminidases. beta-Galactosidase, which was purified more than 11,000-fold, had a substrate specificity rather similar to that of beta-galactosidase from E. coli. This enzyme was inhibited by EDTA and activated by Mn2+, Ca2+, and Mg2+. Problems pertinent to the application of affinity chromatography to the purification of glycosidases are also discussed.
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PMID:Purification and characterization of beta-N-acetylhexosaminidases and beta-galactosidase from Streptococcus 6646 K. 0 84

The functional properties of CZP protein, a mutant deriving from wild-type beta-galactosidase (beta-D-galactoside galactohydrolase; EC 3.2.1.23) by a point mutation, were investigated. A large decrease of the specificity, as evaluated by the kcat/Km ratio, was observed, principally originated by a weaker binding of the substrates. The catalytic constants, whose values are strongly affected by the presence of divalent cations, were smaller or larger for mutant enzyme than for wild-type enzyme, depending upon the experimental conditions. Analysis of the kinetic pathway indicates, with some substrates, a change in the limiting step for the mutant enzyme compared to the wild type. Because the k'3 step is rate limiting for hydrolysis of p-nitrophenyl-beta-D-galactoside by the mutant enzyme in the absence of Mg2+ and its value is relatively small, it is possible to observe a burst of p-nitrophenol during hydrolysis. This provides conclusive evidence for the occurrence of a two-step mechanism, with a sequential release of the products.
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PMID:Functional properties of beta-galactosidase from mutant strain 13 PO of Escherichia coli. 2 41

Growth of Escherichia coli strain MM6-13 (ptsI suc lacI sup), which as a suppressor of the succinate-negative phenotype, was inhibited by lactose. Cells growing in yeast extract-tryptone-sodium chloride medium (LB broth) were lysed upon the addition of lactose. In Casamino Acids-salts medium, lactose inhibited growth, but due to the high K+ content no lysis occurred. Lysis required high levels of beta-galctosidase and lactose transport activity. MM6, the parental strain of MM6-13, has lower levels of both of these activities and was resistant to lysis under these conditions. When MM6 was grown in LB broth with exogenous cyclic adenosine monophosphate, however, beta-galactosidase and lactose transport activities were greatly increased, and lysis occurred upon the addition of lactose. Resting cells of both MM6 and MM6-13 were lysed by lactose in buffers containing suitable ions. In the presence of MG2+, lysis was enhanced by 5 mM KCl and 100 mM NaCl. Higher slat concentrations (50 mM KCl or 200 mM NaCl) provided partial protection from lysis. In the absence of Mg2+, lysis occurred without KCl. Lactose-dependent lysis occurred in buffers containing anions such as sulafte, chloride, phosphate, or citrate; however, thiocyanate or acetate protected the cells from lysis. These data indicate that both cations and anions, as well as the levels of lactose transport and beta-galactosidase activity, are important in lysis.
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PMID:Lysis of Escherichia coli mutants by lactose. 4 Sep 61

1. beta-D-Galactopyranosylmethyl-p-nitrophenyltriazene is an active-site-directed irreversible inhibitor of Mg2+-bound and Mg2+-free lacZ beta-galactosidase from Escherichia coli. 2. The Mg2+-enzyme binds the inhibitor more tightly but the complex then decomposes less rapidly than is the case with Mg2+-free enzyme. 3. Loss of enzyme activity is a linear function of the fraction of enzyme protomers to which are attached beta-D-galactopranosyl[14C]methyl residues: complete inactivation of fully active enzyme results in incorporation of 0.91 equivalent of carbohydrate label per enzyme protomer. 4. When the beta-galactopyranosylmethyl cation is generated in the active site of Mg2+-enzyme, it is captured essentially completely by the protein, but in the active site of Mg2+-free enzyme it is only captured with an efficiency of 25%. 5. Labelled enzyme was carboxymethylated and digested with trypsin; acidic hydrolysis of the isolated tryptic peptide, and field-desorption mass spectrometry of the isolated radioactive derivative, showed it to be 2,5-dioxo-3[2-(beta-D-galactopyranosylmethylthio)ethyl]-1,6-trimethylenepiperazine. 6. This is considered to have arisen from labelling of the sulphur atom of a methionine residue adjacent to a proline residue. 7. The complete amino acid sequence of the molecule [Fowler & Zabin (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 1507-1510] enables the labelled methionine residue to be identified as either Met-421 or Met-500. 8. Sequence data [Fowler, Zabin, Sinnott & Smith (1978) J. Biol. Chem. in the press] show the site of attack to be Met-500.
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PMID:Affinity labelling with a deaminatively generated carbonium ion. Kinetics and stoicheiometry of the alkylation of methionine-500 of the lacZ beta-galactosidase of Escherichia coli by beta-D-galactopyranosylmethyl-p-nitrophenyltriazene. 10 21

1. Removal of Mg2+ from Escherichia coli (lacZ) beta-galactosidase slightly increases the rate of hydrolysis of galactosyl pyridinium salts, but decreases the rate of hydrolysis of arylgalactosides. 2. Fair correlation of logkcat. and log (Km) with the pKa of aglycone is now observed for arglygalactosides, as well as for glycosyl pyridinium salts. 3. Degalactosylation of Mg2+-free enzyme is the rate-limiting step in the hydrolysis of 2,4-dinitrophenyl galactoside. 4. alpha-Deuterium kinetic isotope effects for both sets of substrates are consistent with the rate-determining generation of a glycosyl cation. 5. The pH-independent, SNl hydrolysis of 3,4-dinitrophenyl galactoside has been measured: it is as fast as that of the galactosyl 3-chloropyridinium ion. 6. Hydrolysis of these two substrates by Mg2+-free enzyme proceeds at very similar rates. 7. It is concluded that loss of both types of aglycone takes place, without acid catalysis, from the first ES complex of substrate and apoenzyme. 8. Data for galactosyl azide and thiopicrate confirm that neither charge nor change of atom is the cause of the differences in behavior between aryl galactosides and galactosylpyridinium salts.
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PMID:The necessity of magnesium cation for acid assistance aglycone departure in catalysis by Escherichia coli (lacZ) beta-galactosidase. 10 22

Although the addition of various divalent metals to beta-galactosidase resulted in apparent activation, only Mg2+ and Mn2+ actually did activate. The apparent activation by the other divalent metals was shown to be due to Mg2+ impurities. Calcium did not activate, but experiments suggested that it did bind. Other divalent metals which were studied failed to bind. The dissociation constants for Mg2+ and Mn2+ were 2.8 X 10(-7) and 1.1 X 10(-8) M, respectively, and in each case one ion bound per monomer. These constants corresponded very closely to apparent values which were obtained from activation studies. The apparent binding constant for Ca2+, obtained from competition studies, was 1.5 X 10(-5) M. Data were obtained which showed that Mg2+, Mn2+, and Ca2+ all compete for binding at a single site. Of interest and of possible molecular biological importance was the observation that, while Mg2+ bound noncooperatively (n = 1.0), Mn2+ did so in a highly cooperative manner (n = 3.4). The binding of Mn2+ (as compared to Mg2+) resulted in a twofold drop in the Vmax for the hydrolysis and transgalactosylis reactions of lactose but had little effect on the Vmax of hydrolysis of allolactose, p-nitrophenyl beta-D-galactopyranoside (PNPG), or o-nitrophenyl beta-D-galactopyranoside (ONPG); Km values were not effected differently for any of the substrates by Mn2+ as compared to Mg2+. When very low levels of divalent metal ions were present (0.01 M EDTA added) or when Ca2+ was bound with lactose as the substrate, a greater decrease was observed in the rate of the transgalactosylic reaction than in the rate of the hydrolytic reaction, and the Km values for lactose and ONPG were increased. Of the three divalent metal ions which bound to beta-galactosidase, only Mn2+ had significant stabilizing effects toward denaturing urea and heat conditions.
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PMID:Interaction of divalent cations with beta-galactosidase (Escherichia coli). 11 10

Human adult lung fragments removed from macroscopically undamaged and anthracosis exempted zones of lungs of 20 pneumonectomies made for cancer, were tested for 25 enzymic activities. The location and intensities of these enzymic activities were different in the lung tissue components; The bronchial epithelia contained highly active LDH, MDH, SDH, NADH-TR and NADPH-TR, glucose-6-phosphate dehydrogenase, active hydroxyproline-2-epimerase, alkaline phosphatase. Ca2+-activated ATP-ase, and beta-galactosidase. Bronchial and vascular muscles presented intense activities of LDH, MDH and SDH of alkalinephosphatase, AMP-ase and Ca2+-activated ATP-ase, as well as of beta-galactosidase. The alveolar walls presented high activities of SDH, MDH and LDH, of alkaline and acid phosphatases, of beta-galactosidase and of Tween-40 and 60-esterases, of HEP, cytochrome-oxidase and peroxidase. The free alveolar macrophages were active for LDH, MDH, SDH, NADH-TR and NADPH-TR, G1-6-ph-DH, acid and alkaline phosphatase, cytochrome-oxidase and peroxidase, HEP, AMP-ase and Mg2+-activated ATP-ase, Tween-esterases, naphthol-ASD-acetate esterase, and beta-galactosidase. The endothelia contained high activities of alkaline phosphatase, of AMP-ase and Mg2+-activated ATPase, of LDH, MDH and SDH, and of beta-galactosidase. In bronchial lymphoid nodules it was the LDH, MDH, SDH, cytochrome-oxidase and peroxidase, HEP, alkaline phosphatase and AMP-ase, Tween-60-esterase and beta-galactosidase that were active. The interlobular areas of the lung presented intense activities of SDH, MDH, LDH, HEP and cytochrome-oxidase. The activities of the other tested enzymes were weaker or absent in the adult human lung components, the same as those of aminopeptidases which were present only in some free alveolar macrophages. The discussion of some relationships between these enzymic actitivies and the morphology of the human adult lung tissue asserted that the latter could not be considered as a "normal" tissue but as one overstrained by the components of blood and polluted air.
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PMID:Histoenzymology of the lung. I. Enzyme activities of the lung tissue of acult humans; relationships between structure and functions. 14 Mar 14


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