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. An acid beta-galactosidase, optimum pH4.0-4.5, in the human small-intestinal mucosa was separated and characterized. 2. Autolysis of mucosal homogenates at acid pH inactivated the lactase and hetero beta-galactosidase; the total activity of the acid beta-galactosidase was only slightly depleted, but a greater proportion of the enzyme was solubilized by this treatment. 3. Separation on a Sephadex G-200 column revealed that the acid beta-galactosidase could occur in at least three different forms, probably representing monomer, dimer and octamer or polymer of the enzyme. 4. The properties of the different forms of the acid beta-galactosidase were studied with regard to pH optimum, K(m), rate of hydrolysis of different substrates, and sensitivity to p-chloromercuribenzoate and tris as inhibitors. All these properties were the same for the different forms of the enzyme. 5. The acid beta-galactosidase hydrolyses lactose as well as hetero beta-galactosides and contributes to the lactase activity of intestinal biopsies also when measured at pH 6. This enzyme may therefore be responsible for a considerable part of the residual lactase activity found in lactose-intolerant patients.
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PMID:Human small-intestinal -galactosidases. Separation and characterization of three forms of an acid -galactosidase. 511 32

1. Three fractions of beta-galactosidase activity from the rat small-intestinal mucosa were separated chromatographically. Two of these fractions had an acid pH optimum at 3-4, and the third one had a more neutral pH optimum at 5.7. 2. The two ;acid' beta-galactosidase fractions had considerably lower K(m) values for hetero beta-galactosides than for lactose. The V(max.) values were similar for all the substrates used (lactose, phenyl beta-galactoside, o-nitrophenyl beta-galactoside, p-nitrophenyl beta-galactoside and 6-bromo-2-naphthyl beta-galactoside). No difference could be detected between the two ;acid' fractions with respect to their enzymic properties (pH optimum, K(m) for the different substrates, K(i) for lactose as an inhibitor of the hydrolysis of hetero beta-galactosides, K(i) for phenyl beta-galactoside as an inhibitor of the hydrolysis of lactose, and relative V(max.) for the hydrolysis of different substrates). These two fractions probably represent different forms of the same enzyme. 3. The ;neutral' fraction had similar K(m) values for all the substrates hydrolysed, but with lactose as substrate the V(max.) was much higher than with the hetero beta-galactosides. This fraction did not split phenyl beta-galactoside or 6-bromo-2-naphthyl beta-galactoside at a measurable rate. 4. Lactose was a competitive inhibitor of the hetero beta-galactosidase activities of all the three fractions, and K(i) for lactose as an inhibitor in each case was the same as K(m) for the lactase activity. Phenyl beta-galactoside was a competitive inhibitor of the lactase activity of all the three fractions. These facts strongly indicate that in all the three fractions lactose is hydrolysed by the same active sites as the hetero beta-galactosides. 5. Human serum albumin stabilized the separated enzymes against inactivation by freezing and thawing.
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PMID:Rat small-intestinal beta-galactosidases. Kinetic studies with three separated fractions. 572 84

Previous studies based on work in the rat and preliminary experiments with human intestine have suggested that two beta-galactosidases are present in small intestine, and it is believed that only one of these enzymes is a lactase important for the digestion of dietary lactose. The high prevalence of intestinal lactase deficiency in man prompted more complete study of these enzymes. Human intestinal beta-galactosidases were studied by gel filtration on Sephadex G-200 and Biogel P-300 as well as by density gradient ultracentrifugation. Gel filtration produced partial separation into three peaks of enzyme activity, but much activity against synthetic substrates was lost. Only the trailing peak with specificity for synthetic beta-galactosides was completely separated from the other enzymes. Thus gel filtration was not a suitable preparative procedure for biochemical characterization. Density gradients separated the enzymes more completely, and they were designated according to their sedimentation rates and further characterized. Enzyme I has a molecular weight of 280,000, pH optimum of 6.0, and specificity for lactose of at least five times that for cellobiose or synthetic substrates. A second lactase, enzyme II, possesses slightly greater activity against lactose than for some synthetic substrates and is incapable of splitting cellobiose. Further, it has a lower pH optimum (4.5) and is present in two molecular species (molecular weights 156,000 and 660,000). Enzyme III shows specificity only for synthetic beta-galactosides but has a pH activity curve identical with enzyme I and a molecular weight of 80,000. Whereas human liver and kidney contain a beta-galactosidase with the same biochemical characteristics as intestinal enzyme II, enzymes I and III appear to be peculiar to intestine, and enzyme I most probably represents the lactase of importance in the mucosal digestion of dietary lactose. The following paper considers this further in terms of the biochemical change in intestinal lactase deficiency.
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PMID:Intestinal beta-galactosidases. I. Separation and characterization of three enzymes in normal human intestine. 577 9

Despite the high prevalence of intestinal lactase deficiency in some racial groups and in patients with intestinal disease, the biochemical defect has not been characterized. In the preceding paper normal intestine was found to have two lactases with distinctly different pH optima. Therefore, pH activity curves of homogenates from lactase-deficient intestine were studied, and the pH optimum was found to be shifted from the normal of 5.8 to 4.8. Density gradient ultracentrifugation of intestinal material from five lactase-deficient patients demonstrated absence of a lactase with pH optimum 6.0 and molecular weight 280,000. A second lactase with pH optimum 4.5 and molecular weights of 156,000 and 660,000 remained at normal levels accounting for the shift in the pH optimum in whole intestinal homogenates. In addition, three of the five patients had absence of a smaller beta-galactosidase (molecular weight 80,000) that had specificity only for synthetic substrates. Although not a lactase, this enzyme had a pH optimum identical with the missing lactase, and its activity was inhibited by lactose in a partially competitive manner suggesting that it is capable of binding lactose. It is possible that this enzyme is a precursor or fragment of the missing lactase.The residual lactase activity provided by the lactase with low pH optimum represents 20-70% of the activity of the missing enzyme, and yet these patients are not able to digest dietary lactose. Thus it appears that the residual enzyme plays no significant role in the hydrolysis of ingested lactose.
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PMID:Intestinal beta-galactosidases. II. Biochemical alteration in human lactase deficiency. 577 10

1. Two beta-galactosidases from human small-intestinal mucosa were separated by gel-filtration chromatography and the properties of the two enzymes were studied. Lactose and four hetero beta-galactosides were used as substrates. 2. One of the enzymes was particle-bound and could be partially solubilized with papain. Of the substrates hydrolysed by this enzyme, lactose was hydrolysed most rapidly. This enzyme is thus essentially a disaccharidase and is named lactase. It is presumably identical with the ;lactase 1' described earlier. 3. The other enzyme was mainly soluble and hydrolysed all artificial substrates used, whereas no lactase activity could be detected. This enzyme has therefore been designated hetero beta-galactosidase. 4. p-Chloromercuribenzoate (0.1mm) inhibited the hetero beta-galactosidase completely but did not influence the activity of the lactase. Tris was a competitive inhibitor of both enzymes. 5. The residual lactase activity in the mucosa of lactose-intolerant patients may be exerted by a small amount of remaining lactase as such, or possibly by a third enzyme with a more acid pH optimum.
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PMID:Human small-intestinal beta-galactosidases. Separation and characterization of one lactase and one hetero beta-galactosidase. 582 67

Male Wistar rats (approximately 200 g) were given fibre-free semi-synthetic diets containing either sucrose (S) or a sucrose-starch mixture (SS) as the carbohydrate component, or a diet similar to SS containing 40 g guar gum/kg (G), or 100 g cellulose/kg (C). The animals remained healthy, and weight gain after 30 d was similar in all groups. The small intestines of the animals given diet G were significantly longer than those of the other groups, and showed signs of increased mitotic activity and mucosal growth. No significant differences in mucosal enzyme activity were detected between the two fibre-free control groups. Lactase (EC 3.2.1.23) and alkaline phosphatase (EC 3.1.3.1) activities were significantly lower than controls in group G, but were higher in group C. Kinetic analysis of 3-O-methyl glucose uptake by isolated intestine indicated that the maximum transport rate (Vmax) of tissue from group G tended to be lower than from the fibre-free group SS and group C. It is concluded that materials which are classed as dietary fibre but which differ markedly in their physical properties may also differ in the functional changes to which they give rise in the small intestine. These changes may be at least partially mediated by effects on mucosal cell proliferation.
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PMID:Effect of dietary supplements of guar gum and cellulose on intestinal cell proliferation, enzyme levels and sugar transport in the rat. 609 54

The amounts of lactase (beta-D-galactosidase, EC 3.2.1.23), sucrase (sucrose alpha-D-glucohydrolase, EC 3.2.1.48), maltase (alpha-D-glucosidase, EC 3.2.1.20) microvillus aminopeptidase (EC 3.4.11.2) and dipeptidyl peptidase IV (EC 3.4.14.-) in tangentially sectioned biopsies from jejunum were studied by quantitative immunoelectrophoresis and enzymic assays. All enzymes had their maximum activities near the mid-region of the villi and their lowest activities at the bases of the crypts. The ratio between enzyme activity and immunoreactive protein was constant along the villus-crypt axis. This result is consistent with a continuous brush-border-enzyme synthesis as the enterocytes migrate up the villi.
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PMID:Immunoelectrophoretic studies on human small-intestinal brush-border proteins. 611 34

Preparations of isolated brush border plasma membrane of Hymenolepis diminuta and H. microstoma possess the following enzymatic activities: alkaline phosphohydrolase (E.C. 3.1.3.1); Type I phosphodiesterase (E.E. 3.1.4.1); ribonuclease (E.C. 3.1.4.22); adenosine triphosphatase (E.C. 3.6.1.3); and 5'-nucleotidase (E.C. 3.1.3.5). The following enzymatic activities could not be demonstrated in either membrane preparation: Type II phosphodiesterase (E.C. 3.1.4.18); cyclic adenosine-3', 5'-monophosphate phosphodiesterase (E.C. 3.1.4.17); leucine aminopeptidase (E.C. 3.4.11.1); maltase (alpha-glucosidase; E.C. 3.2.1.20); and lactase (beta-galactosidase; E.C. 3.2.1.23). These data generally agree with those of previous studies in which similar membrane-bound enzymes were demonstrated in intact (living) worms.
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PMID:A comparison of membrane-bound enzymes of the isolated brush border plasma membranes of the cestodes of Hymenolepis diminuta and H. microstoma. 628 Jan 22

The active site-directed inhibitor 4-nitrophenyl-beta-D-galactopyranosylmethyltriazene, previously shown (Fowler, A. V., Zabin, I., Sinnott, M. L., and Smith, P. J. (1978) J. Biol. Chem. 253, 5283-5285) to alkylate methionine 502 in lacZ beta-galactosidase, was used to label the second naturally occurring beta-galactosidase of Escherichia coli (ebgo). The reagent was also used to label two mutant forms of the enzyme (ebga and ebgb) selected for enhanced lactase activity. In the case of ebgo and ebga, 75 and 85% of the label, respectively, was incorporated into a tryptic peptide which is homologous (38% identity) to residues 483-503 of the lacZ beta-galactosidase sequence. In the ebgo and ebga enzymes, a serine probably is alkylated. In the case of the ebgb enzyme, 61% of the label is found on a tryptic peptide homologous (69% identity) with residues 457-468 of the lacZ beta-galactosidase. In this peptide, a glutamic acid and a tyrosine residue are both alkylated.
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PMID:The active site regions of lacZ and ebg beta-galactosidases are homologous. 641 10

The beta-galactosidase activities of the rabbit small intestinal mucosa were studied over the pH range of 2.6 to 8.4, using different substrates, and in the presence or absence of the enzyme inhibitor p-chloromercuribenzoic acid. The results indicated the presence of 4 beta-galactosidases: (i) a neutral beta-galactosidase (lactase) with optimum pH of 5.8, (ii) an acid beta-galactosidase I with optimum pH of 3.4, (iii) an acid beta-galactosidase II with optimum pH of 4.6, and (iv) a hetero beta-galactosidase with pH optimum of 7.6. Seemingly, 3 of these beta-galactosidases were comparable with those in other mammals, and the 4th has not been reported in other species.
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PMID:Rabbit small intestinal beta-galactosidases. 642 19


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