Methionine Transport in Salmonella typhimurium: Evidence for at Least One Low-affinity Transport System

Abstract

The systems which transport methionine in Salmonella typhimurium LT2 have been studied. Fourteen mutants, isolated by three different selection procedures, had similar growth characteristics and defects in the specific transport process showing a Km of 0 . 3 ,~~ for L-methionine, and therefore lack the high-affinity, metP transport system. The sites of mutation in four of the mutants were shown by P1-mediated transduction to be linked (0-3 to 1.1 %) with a proline marker located at unit 7 on the S. typhimurium chromosome. The high-affinity system was subject to both repression and transinhibition by methionine, and it may also be regulated by the metJ and metK genes. There appeared to be at least two additional transport systems with relatively low affinities for methionine in the metP763 mutant strain, with apparent Km values for methionine of 24 ,UM and approximately 1.8 mM. The latter system, with a very low affinity for methionine, was inhibited by leucine. In addition, methionine inhibited leucine transport, suggesting that one of the low-affinity methionine transport systems may actually be a leucine transport system.

The Study of Methionine Uptake inSaccharomyces cerevisiaeReveals a New Family of Amino Acid Permeases

“…The activity of one of the low affinity permeases is strongly inhibited by L-leucine and leucine transport is inhibited by L-methionine. The authors thus suggested that one of the low affinity methionine transport systems could actually be a leucine transport system (Ayling et al, 1979). In S. cerevisiae, the uptake of branched chain amino acids is still under study.…”

Functional Demonstration of Reverse Transsulfuration in the Mycobacterium tuberculosis Complex Reveals That Methionine Is the Preferred Sulfur Source for Pathogenic Mycobacteria

“…In the presence of methionine, weak (about 2-fold) repression of sulfate transport occurred (4) so tubercle bacteria would take up methionine 5-6ϫ faster than sulfate at the estimated physiological concentration. Although the genes that encode the methionine transporter were not identified (2), there are candidates among the many predicted ABC transporters for amino acid, including methionine, transport (37)(38)(39).…”

Fine structure mapping and complementation studies of themetDmethionine transport system inSalmonella typhimurium

“…It had previously been shown that mutations in 14 strains which were resistant to the inhibitory methionine analogues a-methylmethionine (AM) or methionine sulphoximine (METX), and which failed to grow on D-methionine, mapped in the metD locus at min 6 on the Salmonella linkage map; all these mutations resulted in reduced transport of L-and Dmethionine (Ayling et al 1979;Sanderson & Roth, 1988). A deletion map has now been constructed and about 100 newly-isolated point mutations have been located on the map (Fig.…”

“…metD deletion strains were identified as those strains which, when used as recipients in spot transduction against ten randomly selected metD point mutants as donors, produced two or more negative results; these negative results were confirmed using a whole plate for each transduction cross. Uptake of L-[ 14 C]methionine was determined using a rapid procedure (Ayling et al 1979). …”

“…L-and D-methionine are transported into Salmonella typhimurium by the metD high-affinity system (Ayling & Bridgeland, 1972;Ayling et al 1979). This system was originally called the metP system, but was renamed metD (Shaw & Ayling, 1991), to conform with usage for the analogous system in Escherichia coli (Kadner, 1977;Bachmann, 1990).…”