Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Studies showed that the plant cell wall polysaccharide arabinogalactan supported growth of Bifidobacterium longum in batch culture. Galactose was also utilized, but not arabinose, the other major constituent sugar of the polymer. Enzymes required for hydrolysis of arabinogalactan ('arabinogalactanase', alpha-arabinopyranosidase, beta-galactosidase) were inducible and cell-associated in B. longum, and their expression was repressed by glucose. Considerable amounts of alpha-arabinopyranosidase and beta-galactosidase were synthesized during growth on arabinogalactan, but only low levels of arabinogalactanase were detected. B. longum only grew on arabinogalactan in continuous culture under putative carbon-excess conditions. In C-limited chemostats, the bifidobacterium could not establish unless Bacteroides thetaiotaomicron was present in co-culture. The relationship between the two organisms was not simply commensal; at low specific growth rates, bacteroides cell population densities were approximately 30% lower than those recorded in axenic culture, indicating the existence of competitive interactions with the bifidobacterium. In contrast, at high specific growth rates, a mutualistic association was observed, in that Bact. thetaiotaomicron was maintained in the chemostats at high dilution rates if bifidobacteria were also present. Measurements of residual carbohydrate in spent culture fluid from C-limited chemostats indicated that a large part of the arabinogalactan molecule could not be broken down by either B. longum or Bact. thetaiotaomicron alone, or in co-culture. Formate and acetate were the major fermentation products of B. longum cultured in the presence of high concentrations of arabinogalactan, confirming that these bacteria were growing under energy-limited conditions.
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PMID:Arabinogalactan utilization in continuous cultures of Bifidobacterium longum: effect of co-culture with Bacteroides thetaiotaomicron. 1688 14

The open reading frames of tomato beta-galactosidase (TBG) 4 and 5 cDNAs were expressed in yeast, and the enzymes properties and substrate specificities were investigated. The two enzymes had peak activities between pH 4-4.5 and 37-45 degrees C. TBG4 specifically hydrolyzed beta-(1-->4) and 4-linked galactooligosaccharides. TBG5 had a strong preference to hydrolyze beta-(1-->3) and beta-(1-->6)-linked galactooligosaccharides. Exo-beta-galactanase activity of the TBG enzymes was measured by determining the release of galactosyl residues from native tomato cell wall fractions throughout fruit development and ripening. Both TBGs released galactose from all of the fractions and stages tested. TBG4 activity was highest using chelator soluble pectin and alkali soluble pectin at the turning stage of ripening. Using aminopyrene trisulfonate labeled substrates, TBG4 was the only enzyme with strong exo-beta-(1-->4)-galactanase activity on 5 mer or greater galactans. TBG4 and TBG5 were both able to degrade galactosylated rhamnogalacturonan. Neither enzyme was able to degrade galactosylated xyloglucan.
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PMID:Enzymatic activity and substrate specificity of recombinant tomato beta-galactosidases 4 and 5. 1898 78


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