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  • 1
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two classes of negative mutants in the hexuronate system of Escherichia coli K 12 were isolated and characterized. Strains of the first class were specifically deficient in the enzyme uronic isomerase. They did not grow on galacturonate or glucuronate, the substrates of isomerase, but very well developped on the products, tagaturonate or fructuronate. In these mutants, keto-but not aldo-hexuronates could still induce other enzymes of the hexuronate system. The corresponding mutations mapped in the uxa C locus and were localized by sexual crosses and P1 transduction near min 60, between tol C and arg G markers. The uxa C locus was very closely linked to the uxa A locus, the structural gene for altronic hydrolyase. Biochemical characterizations of uxa C mutants using temperature sensitive revertants was achieved by means of thermal inactivation and kinetic studies. Results indicated that the uxa C locus was the structural gene for uronic isomerase. Mutant strains of the second class were unable to develop on galacturonate or tagaturonate but normally grew on glucuronate. They were specifically deficient in the enzyme altronic oxidoreductase which is the following functional enzyme, after isomerase, in galacturonate catabolism. The corresponding mutations were localized by interrupted and non-interrupted conjugations. They all mapped in the uxa B locus near 45 min. Biochemical studies of altronic oxidoreductase residual activities in uxa B mutants strongly suggested that the uxa B locus was the structural gene for altronic oxidoreductase. A direct method for the estimation of uronic isomerase using aldonic oxidoreductases as coupling enzymes was described and routinely applied to characterize hexuronate system mutants.
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  • 2
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutants of E. coli specifically deficient for the enzyme altronic hydrolyase have been isolated. These strains are unable to metabolize galacturonate but still normally grow on glucuronate; inducibility for the other galacturonate-induced enzymes is not modified. The position of these mutations called “uxaA” locus in relation to the argG, tolC and metC markers was established both by sexual crosses and by P1 transduction; evidence is presented that uxaA is located between argG and tolC. Biochemical characterization of uxaA mutants using thermosensible revertants or mutants was achieved by means of thermal inactivation and kinetic parameters determination. Experimental results strongly suggest that uxaA locus is the structural gene of the altronic hydrolyase enzyme.
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  • 3
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutants of E. coli specifically deficient for the enzyme mannonic hydrolyase have been isolated. These strains are unable to metabolize glucuronate but still normally grow on galacturonate; inducibility for the other glucuronate-induced enzymes is not modified. The position of these mutations called “uxuA” locus in relation to the pyrB-guaC region, and probably near 85.5 minutes, was established by sexual crosses and by P1 transduction Biochemical characterization of uxuA mutants using thermosensible mutants was achieved by means of thermal inactivation and kinetic studies. Experimental results strongly suggest that uxuA locus is the structural gene of the mannonic hydrolyase.
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  • 4
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In a study of the regulation of the hexuronate system in Escherichia coli K 12, two classes of glucuronate negative mutants were isolated and characterized. The first class was composed of eight mutants specifically deficient for the enzyme mannonic oxidoreductase. Glucuronate via fructuronate could still induce the other four hexuronate system enzymes in these strains although it was no more metabolized; galacturonate is normally used. The corresponding mutations in the uxu B locus were localized on the chromosome of E. coli by interrupted and non-interrupted conjugations. They all mapped at 86 min close to the uxu A locus, the structural gene of mannonic hydrolase which is the following functional enzyme in glucuronate catabolism. Biochemical characterizations of uxu B mutants using thermal inactivation and pCMB inhibition of residual mannonic oxidoreductase activity, as well as dominance studies with diploid strains strongly suggested that the uxu B locus was the structural gene of mannonic oxidoreductase. The second class of mutations involved pleiotropic deficiency in both mannonic oxidoreductase and hydrolyase. Their genetic mapping and the preliminary fine structure analysis of the uxu region showed they were deletions extending into uxu A and uxu B genes. These properties agreed very well with independent physiological results (Robert-Baudouy, Portalier et Stoeber, 1973) and was in agreement with the existence of an unique operon at least composed of uxu A and uxu B structural genes.
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