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)

Exo-galactanase/beta-galactosidase (EC 3.2.1.23) activity is thought to be responsible for the loss of galactosyl residues from the cell walls of ripening tomatoes. Transgenic tomato plants (Lycopersicon esculentum Mill cv. Ailsa Craig) with reduced exo-galactanase/beta-galactosidase mRNA were generated to test this hypothesis and to investigate the role of the enzyme in fruit softening. A previously identified tomato beta-galactosidase cDNA clone, TBG1, was used in the experiments. Heterologous expression of the clone in yeast demonstrated that TBG1 could release galactosyl residues from tomato cell wall galactans. Transgenic plants showed a reduction in TBG1 mRNA to 10% of normal levels in the ripening fruits. However, despite the reduction in message, total beta-galactosidase and exo-galactanase activities were unaffected. Furthermore, there was no apparent effect on levels of cell wall galactosyl residues when compared with the control. It was concluded that during the ripening of tomato fruits a family of beta-galactosidases capable of degrading cell wall galactans are active and down-regulation of TBG1 message to 10% was insufficient to alter the degree of galactan degradation.
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PMID:Down-regulation of a ripening-related beta-galactosidase gene (TBG1) in transgenic tomato fruits. 1141 2

Galactosyltransferases (GalTs), capable of transferring a galactosyl residue from UDP-galactose (UDP-Gal) to polysaccharide acceptor, were solubilized from flax (Linum usitatissimum L.) membranes using 0.5% CHAPS. The observed requirement for a rhamnogalacturonan I (RG-I) exogenous substrate to stimulate the solubilized GalT activity provided the first evidence for the presence of RG-I GalT activities in flax cells. An assay to measure specifically the products of this RG-I GalT activity was designed, based on size-exclusion chromatography. Labelled products were characterized as an RG-I polymer by using purified RG-I hydrolase or lyase. At pH 8 and in the presence of 5 mM CaCl2, beta-D-galactosyl residues were specifically transferred onto RG-I branches of short beta-(1 --> 4)-D-galactan side chains. These side chains were liable to hydrolysis by beta-galactosidase and endo-beta-(1 --> 4)-D-galactanase. The RG-I GalT had a temperature optimum of 30 degrees C. an apparent Km for UDP-Gal and exogenous RG-I substrate of 460 +/- 40 microM and 1.1 +/- 0.1 mg ml(-1) respectively, and a Vmax of 3.0 +/- 0.5 pkat mg(-1) protein.
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PMID:Solubilization of rhamnogalacturonan I galactosyltransfrases from membranes of a flax cell suspension. 1150 67

During ripening of grape (Vitis vinifera L.) berries, softening occurs concomitantly with the second growth phase of the fruit and involves significant changes in the properties of cell wall polysaccharides. Here, the activities of enzymes that might participate in cell wall modification have been monitored throughout berry development. Alpha-galactosidase (EC 3.2.1.22), beta-galactosidase (EC 3.2.1.23) and pectin methylesterase (EC 3.1.1.11) activities were present, but no polygalacturonase (EC 3.2.1.15), cellulase (EC 3.2.1.4), xyloglucanase (xyloglucan-specific cellulase EC 3.2.1.4) or galactanase (EC 3.2.1.89) could be detected. The accumulation of mRNAs encoding wall-modifying enzymes was examined by northern hybridization analysis. Transcripts for beta-galactosidase, pectin methylesterase, polygalacturonase, pectate lyase (EC 4.2.2.2) and xyloglucan endotransglycosylase (EC 2.4.1.207) were present during ripening, although polygalacturonase activity had not been detected in berry extracts. Cellulases could not be detected in ripening berries, either at the enzyme or mRNA levels. The increase in beta-galactosidase activity and mRNA is consistent with the observed decrease in type-I arabinogalactan content of the walls during ripening, and the detection of polygalacturonase and pectate lyase mRNAs might explain the increased solubility of galacturonan in walls of ripening grapes. Thus, the modification of cell wall polysaccharides during softening of grape berries is a complex process involving subtle changes to different components of the wall, and in many cases only small amounts of enzyme activity are required to effect these changes.
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PMID:Expression patterns of cell wall-modifying enzymes during grape berry development. 1180 Mar 90

Transcript abundance of the gene encoding beta-galactosidase II, a beta-galactosidase/exo-galactanase (EC 3.2.1.23) present during tomato (Lycopersicon esculentum) fruit ripening, was suppressed by expression of an antisense tomato beta-galactosidase 4 (TBG4) cDNA driven by the cauliflower mosaic virus 35S promoter. RNA gel-blot analysis was used to evaluate TBG4 mRNA levels in transgenic fruit. All of the antisense lines had attenuated TBG4 mRNA levels in turning stage fruit; however, TBG4 mRNA suppression was unstable, and mRNA levels varied in red-ripe fruit among the lines. Suppression of TBG4 mRNA levels in antisense fruit was correlated with a reduction in extractable exo-galactanase activity against a lupin galactan. All of the antisense lines had reduced free galactose levels at mature green stage 4, but levels comparable with controls during ripening. Total cell wall galactosyl contents in the antisense fruit were not significantly different from control fruit. Whole-fruit firmness was measured using a texture analyzer and the means of the peak force measurements for four of six antisense lines were significantly higher than control fruit. One antisense line had red-ripe fruit that were 40% firmer than controls. Fruit from this antisense line also had the lowest TBG4 mRNA and exo-galactanase levels and the highest wall galactosyl content during the early stages of ripening, implicating an involvement of this gene product in cell wall modification leading to fruit softening.
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PMID:Down-regulation of tomato beta-galactosidase 4 results in decreased fruit softening. 1217 88

The fruit extracts of ripening cv. Japanese Persimmon, "Saijyo", contained a number of glycosidases and glycanases. Among them, beta-galactosidase appeared to be the most significant, and the activity increased in parallel with tissue ripening. Persimmon beta-galactosidase was presented in at least three isoforms, beta-galactosidase-I (pI = 4.88), beta-galactosidase-II (pI = 6.76), and beta-galactosidase-III (pI = 7.05). beta-Galactosidase-III had exo-type galactanase activity, while the others did not. The activity of endo-type glycanases was a maximum in immature green or yellow fruits. The firmness of the pulp tissue decreased dramatically, and the amount of water-soluble polysaccharide (WSS) increased. The enzyme activities of exo-type glycosidases, especially beta-galactosidase, appeared maximal in mature red fruits. The amount of extractable pectin remained unchanged, although the galactose content of the high-molecular-weight fraction in WSS decreased dramatically. These results suggest that the ripening of persimmon was caused by the solubilization of pectic polysaccharide by endo-type glycanases and digestion by exo-type glycosidases. beta-Galactosidase, in particular, seemed to play a major role in ripening the fruit.
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PMID:beta-Galactosidase and its significance in ripening of "Saijyo" Japanese Persimmon fruit. 1261 75

Antisense suppression of a tomato beta-galactosidase gene (TBG6) was used to study its role in fruit development, cell wall-modification, and fruit firmness. TBG6 mRNA is highly abundant during the early stages of fruit development, but the levels decline sharply after the breaker stage with the start of the respiratory climacteric and a concomitant increase in ethylene production. Two antisense lines were obtained with significantly reduced levels of TBG6 mRNA at all stages of fruit development. At 30 d after pollination (dap), TBG6 mRNA levels were reduced by up to 98% and 88% in lines 6-2 and 6-10, respectively. Morphological phenotypes observed in the antisense lines included increased fruit cracking, reduced locular space, and a doubling in the thickness of the fruit cuticle. Two biochemical changes in antisense lines, compared with wild-type lines, were a reduction of exo-galactanase activity at the breaker +3 d stage and a reduction in the cell wall galactosyl content at the 20 dap stage. In addition, transgenic lines exhibited a 35-39% reduction in fruit firmness at the 20 dap stage, but their texture was equivalent to the wild type at 30 dap and beyond. Although the exact function of the TBG6 product is still unknown, these results implicate an important role for this enzyme in early fruit growth and development in tomato.
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PMID:Antisense suppression of a beta-galactosidase gene (TB G6) in tomato increases fruit cracking. 1286 45

Galactosyltransferase (GalT) activity that results in the transfer of galactose (Gal) from UDP-Gal to exogenous (1-->4)-beta-galactooligosaccharides labeled with 2-aminobenzamide (2AB) at their reducing ends was identified in a particulate preparation obtained from 2-day-old mung bean (Vigna radiata L. Wilezek) hypocotyls. The enzymes responsible were shown, by high-performance anion-exchange chromatography and normal-phase liquid chromatography-electrospray ionization mass spectrometry, to transfer up to eight Gals to the non-reducing end of 2AB-labeled galactooligosaccharide. Using 1H nuclear magnetic resonance spectroscopy, and beta-galactosidase and endo-beta-(1-->4)-galactanase treatments of the enzymatically formed 2AB-labeled galactooligosaccharides, the newly incorporated Gal residues were shown to be beta-(1-->4) linked. Time-course studies indicated that at least two different types of GalT isoform are involved in the elongation of the acceptor substrates. 2AB-labeled galactoheptaose was the most effective acceptor substrate analyzed, although galactooligosaccharides with a degree of polymerization between 4 and 6 were also acceptor substrates. 2AB-labeled penta- and heptasaccharides (RG5 and RG7) generated from rhamnogalacturonan I (RG-I) were not acceptor substrates, suggesting that the GalTs were not capable of adding Gal residues directly to the RG-I backbone. Maximum GalT activity was obtained at pH 6.5 and 20 degrees C in the presence of 25 mM Mn2+ and 0.75% (w/v) Triton X-100. The enzyme had an apparent Km of 20 microM for 2AB-labeled galactoheptaose and 32 microM for UDP-Gal. The characteristics of the enzyme in mung bean microsomal membranes and the usefulness of fluorogenic 2AB-labeled galactooligosaccharides for the assay of GalT are discussed.
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PMID:Identification of elongating beta-1,4-galactosyltransferase activity in mung bean (Vigna radiata) hypocotyls using 2-aminobenzaminated 1,4-linked beta- D-galactooligosaccharides as acceptor substrates. 1498 44

The potential significance of the previously reported papaya (Carica papaya L.) beta-galactosidase/galactanase (beta-d-galactoside galactohydrolase; EC 3.2.1.23) isoforms, beta-gal I, II and III, as softening enzymes during ripening was evaluated for hydrolysis of pectins while still structurally attached to unripe fruit cell wall, and hemicelluloses that were already solubilized in 4 M alkali. The enzymes were capable of differentially hydrolyzing the cell wall as evidenced by increased pectin solubility, pectin depolymerization, and degradation of the alkali-soluble hemicelluloses (ASH). This enzyme catalyzed in vitro changes to the cell walls reflecting in part the changes that occur in situ during ripening. beta-Galactosidase II was most effective in hydrolyzing pectin, followed by beta-gal III and I. The reverse appeared to be true with respect to the hemicelluloses. Hemicellulose, which was already released from any architectural constraints, seemed to be hydrolyzed more extensively than the pectins. The ability of the beta-galactanases to markedly hydrolyze pectin and hemicellulose suggests that galactans provide a structural cross-linkage between the cell wall components. Collectively, the results support the case for a functional relevance of the papaya enzymes in softening related changes during ripening.
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PMID:Papaya beta-galactosidase/galactanase isoforms in differential cell wall hydrolysis and fruit softening during ripening. 1569 77

A basic beta-galactosidase with high specificity toward beta-(1-->3)- and beta-(1-->6)-galactosyl residues was cloned from radish (Raphanus sativus) plants by reverse transcription-PCR. The gene, designated RsBGAL1, contained an open reading frame consisting of 2,532 bp (851 amino acids). It is expressed in hypocotyls and young leaves. RsBGAL1 was highly similar to beta-galactosidases having exo-beta-(1-->4)-galactanase activity found in higher plants and belongs to family 35 of the glycosyl hydrolases. Recombinant RsBGAL1 was expressed in Pichia pastoris and purified to homogeneity. The recombinant enzyme specifically hydrolyzed beta-(1-->3)- and beta-(1-->6)-galactooligosaccharides, the same substrates as the native enzyme isolated from radish seeds (Sekimata et al., 1989). It split off about 90% of the carbohydrate moieties of an arabinogalactan protein extracted from radish roots in concerted action with microbial alpha-l-arabinofuranosidase and beta-glucuronidase. These results suggest that RsBGAL1 is a new kind of beta-galactosidase with different substrate specificity than other beta-galactosidases that exhibit exo-beta-(1-->4)-galactanase activity. The C-terminal region (9.6 kD) of RsBGAL1 is significantly similar to the Gal lectin-like domain, but this region is not retained in the native enzyme. Assuming posttranslational processing of RsBGAL1 with elimination of the Gal lectin-like domain results in a protein consisting of two subunits with molecular masses of 46 and 34 kD (calculated from the RsBGAL1 gene sequence). This is in good agreement with the SDS-PAGE and matrix-assisted laser desorption/ionization-time-of flight mass spectrometry measurements for subunits of the native enzyme (45 and 34 kD) and may thus partially explain the formation process of the native enzyme.
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PMID:Molecular cloning of a {beta}-galactosidase from radish that specifically hydrolyzes {beta}-(1->3)- and {beta}-(1->6)-galactosyl residues of Arabinogalactan protein. 1598 Jan 90

We report the generation of Solanum tuberosum transformants expressing Cicer arietinum betaIII-Gal. betaIII-Gal is a beta-galactosidase able to degrade cell wall pectins during cell wall loosening that occurs prior to cell elongation. cDNA corresponding to the gene encoding this protein was identified among several chickpea beta-galactosidase cDNAs, and named CanBGal-3. CanBGal-3 cDNA was expressed in potato under the control of the granule-bound starch synthase promoter. Three betaIII-Gal transformants with varying levels of expression were chosen for further analysis. The transgenic plants displayed no significant altered phenotype compared to the wild type. However, beta-galactanase and beta-galactosidase activities were increased in the transgenic tuber cell walls and this affected the potato tuber pectins. A reduction in the galactosyl content of up to 50% compared to the wild type was observed in the most extreme transformant, indicating a reduction of 1,4-beta-galactan side-chains, as revealed by analysis with LM5 specific antibodies. Our results confirm the notion that the pectin-degrading activity of chickpea betaIII-Gal reported in vitro also occurs in vivo and in other plants, and confirm the involvement of betaIII-Gal in the cell wall autolysis process. An increase in the homogalacturonan content of transgenic tuber cell walls was also observed by Fourier transform infrared spectroscopy (FTIR) analysis.
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PMID:In vivo expression of a Cicer arietinum beta-galactosidase in potato tubers leads to a reduction of the galactan side-chains in cell wall pectin. 1607 77


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