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The utilisation of d-galactonate and d-2-oxo-3-deoxygalactonate by Escherichia coli K-12
Authors:Ronald A Cooper
Institution:1. Department of Biochemistry, University of Leicester, University Road, LE1 7RH, Leicester, England
Abstract:
  1. Escherichia coli K-12 mutants unable to grow on d-galactonate have been isolated and found to be defective in either galactonate dehydratase, 2-oxo-3-deoxygalactonate 6-phosphate aldolase or devoid of both of these enzymes and of 2-oxo-3-deoxygalactonate kinase.
  2. 2-Oxo-3-deoxygalactonate kinase and 2-oxo-3-deoxygalactonate 6-phosphate aldolase are still induced by galactonate in mutants lacking galactonate dehydratase, suggesting that galactonate rather than a catabolic product of galactonate is the inducer of the galactonate catabolic enzymes. Synthesis of the enzymes is subject to glucose catabolite repression.
  3. Mutants defective in 2-oxo-3-deoxygalactonate 6-phosphate aldolase accumulate 2-oxo-3-deoxygalactonate 6-phosphate when exposed to galactonate and this compound causes general growth inhibition.
  4. Secondary mutants that no longer show this inhibition fail to make 2-oxo-3-deoxygalactonate 6-phosphate due to additional defects in galactonate transport, galactonate dehydratase, 2-oxo-3-deoxygalactonate kinase or a putative promoter mutation that prevents formation of these enzymes.
  5. A spontaneous mutant capable of growth on 2-oxo-3-deoxygalactonate has been isolated. It has two genetically distinct mutations. One permits constitutive formation of the galactonate catabolic enzymes and the other allows the uptake of 2-oxo-3-deoxygalactonate. Neither mutation on its own permitted growth on 2-oxo-3-deoxygalactonate.
  6. Genes specifying the various galactonate catabolic enzymes have been located at min 81.7 on the E. coli K-12 linkage map and probably constitute an operon. The gene sequence in this region was shown to by: pyrE uhp dgo dnaA.
Keywords:
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