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. Two spontaneous Escherichia coli K12 mutants resistant to glucose catabolite repression were isolated using minimal agar plates with methyl alpha-D-glucoside. Mutants grow well on glucose and mannitol. 2. Glucose does not inhibit the inducible enzyme synthesis in isolated mutants: mutant cell (in contrast to parent cells) produce high levels of beta-galactosidase and L-tryptophanase under the conditions of glucose catabolite repression. 3. The isolated mutants are negative in methyl-alpha-D-glucoside transport; glucose uptake is not severely damaged. But the mutants (named tgl, transport of glucose) retained the ability to phosphorylate methyl alpha-D-glucoside in vitro at the expense of phosphoenolpyruvate. 4. The tgl mutation is cotransduced with purB and pyrC markers, i.e. locates near 24 min of the E. coli chromosome map. 5. It is thought that E. coli cells possess two glucose transport systems. The first one is represented by the glucose-specific enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system. The second glucose transport system (coded for tgl gene) functions as permease and possesses high affinity to methyl alpha-D-glucoside. The integrity of glucose permease determine the sensitivity of the cell to glucose catabolite repression.
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PMID:Glucose catabolite repression in Escherichia coli K12 mutants defective in methyl-alpha-d-glucoside transport. 109 69

In gram-positive bacteria, HPr, a phosphocarrier protein of the phosphoenolpyruvate:sugar phosphotransferase system (PTS), is phosphorylated by an ATP-dependent, metabolite-activated protein kinase on seryl residue 46. In a Bacillus subtilis mutant strain in which Ser-46 of HPr was replaced with a nonphosphorylatable alanyl residue (ptsH1 mutation), synthesis of gluconate kinase, glucitol dehydrogenase, mannitol-1-P dehydrogenase and the mannitol-specific PTS permease was completely relieved from repression by glucose, fructose, or mannitol, whereas synthesis of inositol dehydrogenase was partially relieved from catabolite repression and synthesis of alpha-glucosidase and glycerol kinase was still subject to catabolite repression. When the S46A mutation in HPr was reverted to give S46 wild-type HPr, expression of gluconate kinase and glucitol dehydrogenase regained full sensitivity to repression by PTS sugars. These results suggest that phosphorylation of HPr at Ser-46 is directly or indirectly involved in catabolite repression. A strain deleted for the ptsGHI genes was transformed with plasmids expressing either the wild-type ptsH gene or various S46 mutant ptsH genes (S46A or S46D). Expression of the gene encoding S46D HPr, having a structure similar to that of P-ser-HPr according to nuclear magnetic resonance data, caused significant reduction of gluconate kinase activity, whereas expression of the genes encoding wild-type or S46A HPr had no effect on this enzyme activity. When the promoterless lacZ gene was put under the control of the gnt promoter and was subsequently incorporated into the amyE gene on the B. subtilis chromosome, expression of beta-galactosidase was inducible by gluconate and repressed by glucose. However, we observed no repression of beta-galactosidase activity in a strain carrying the ptsH1 mutation. Additionally, we investigated a ccpA mutant strain and observed that all of the enzymes which we found to be relieved from carbon catabolite repression in the ptsH1 mutant strain were also insensitive to catabolite repression in the ccpA mutant. Enzymes that were repressed in the ptsH1 mutant were also repressed in the ccpA mutant.
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PMID:Loss of protein kinase-catalyzed phosphorylation of HPr, a phosphocarrier protein of the phosphotransferase system, by mutation of the ptsH gene confers catabolite repression resistance to several catabolic genes of Bacillus subtilis. 819 89