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Two mutants of Salmonella typhimurium LT2, strains SM64 and SM166, unable to use succinate, fumarate, or malate as carbon sources for growth, were isolated by treatment with N-methyl-N'-nitro-N-nitrosoguanidine.
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Mutant cells, induced aerobically in any of the Ca~dicarboxylic acids, presented all the enzymes of the I~'ebs cycle, as well as the phosphoenolpyruvatc earboxykinase (required for growth in these substrates), with the same activities as those found in the parental LT2 strain.
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The mutants presented a deficient transport system for the C4-dicarboxylic acids. The kinetics of induction of the transport system, as well as some of its characteristics, were studied in the parental and mutant strains. Also the chromosomal site dct, responsible for the deficiency observed in the mutants, was located and found to be cotransducible with locus xyl.
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From biochemical and genetic studies it is concluded that in S. typhimurium the transport of the Cr acids succinie, fumaric, and malic is carried out by a single transport system, common for the three substrates.
The metabolism of the C4-dicarboxylic acids succinic, fumaric, and malic in Escherichia coli has been thoroughly studied, both in the aspect of their transport through the cell membrane (Kay and Kornberg, 1969Kornberg, , 1971)), as well as in the enzymatic make up of the cells required for their utilization as carbon sources (Halpern et al., 1964;Gray et al., 1966;Hanson and Cox, 1967).
In the case of Salmonella typhimurium, which can use the C4-dicarboxylic acids for growth, there is only a report about the enzyme profile of the cells grown with succinate as carbon source (Parada et al., 1973),