Salmonella typhimurium biosynthesis

Salmonella typhimurium mutant.136-149 The defect of this mutant lies in the apparent KM (D-arabinose 5-phosphate) of its KDO 8-phosphate synthetase (compare this Section, 2). This KM increases more than 25-fold between 29 and 42°, so that the cells become increasingly dependent on exogenously supplied D-arabinose 5-phosphate as the growth temperature is raised. Cessation of LPS biosynthesis under nonper-missive conditions is accompanied by the accumulation of a KDO-de-ficient, precursor molecule.149 Lehmann150 and Rick and coworkers151 described studies directed at the isolation and chemical characterization of such lipid A precursors (for example, 133, Scheme 39). The... 

As an offshoot of studies of genes concerned with the biosynthesis of amino acids, a range of E. coli (see, e.g., Yanofsky, 1971) and Salmonella typhimurium strains (see, e.g., Ames, 1971) with relatively well-defined mutations in known genes... 

Genetic Make up of Tester Strains. The most widely used strains are those developed by Bruce Ames and colleagues which are mutant derivatives of the organism Salmonella typhimurium. Each strain carries one of a number of mutations in the operon coding for histidine biosynthesis. In each case the mutation can be reverted either by base-change or by frameshift mutations. The genotype of the commonly used strains is shown in Table 6.6. 

C. R. H. Raetz, in C. Neidhardt, J. 1. Ingraham, K. Brooks Low, B. Magasanik, M. Schaechter, and H. E. Umbarger (Eds.), Escherichia coli and Salmonella typhimurium Cellular and Molecular Biology Structure and Biosynthesis of Lipid A, p. 498. American Society of Microbiologists, Washington DC, 1987. 

Hydrogenase isoenzymes are also common among the metabolically more versatile bacteria (see Chapter 2). For instance, H2 metabolism and isoenzyme composition in enteric bacteria, including Escherichia coli and Salmonella typhimurium, appear to be differentially regulated under the two modes of anaerobic life, fermentation and anaerobic respiration (Table 3.1). Furthermore, biosynthesis of the individual isoenzymes appears to be controlled at a global level by the quality of the carbon source. 

Regulation of histidine synthesis. In all, ten different genes code for the enzymes of histidine biosynthesis in Salmonella typhimurium. They are clustered as the histidine operon, a consecutive series of genes which are transcribed into messenger RNA as a unit.250 251 The gene symbols His A, HisB, etc., are indicated in Fig. 25-13, and their positions on the E. coli gene map are indicated in Fig. 26-4. The gene HisB codes for a complex protein with two different enzymatic activities as shown in Fig. 25-13. 

The first two steps in the biosynthesis of tryptophan in Salmonella typhimurium involve the enzyme complex anthranilate synthase-phosphoribosyltransferase, which is a tetramer having two subunits of each enzyme. The anthranilate synthase catalyzes reaction (7) and the phos-phoribosyltransferase catalyzes two reactions the N-terminal portion cleaves glutamine to glutamate giving NH3 for the anthranilate synthase, while the C-terminal portion catalyzes reaction (8).3,1,312 All these reactions require M2+ cations. Orotate phosphoribosyltransferase binds four Mn2+ ions in a cooperative fashion kinetic data have been interpreted in a scheme where both metal-free and metal-containing enzyme catalyze the reaction.313... 

The isolation and purification of the enzymes involved in KDO biosynthesis was necessary for the study of potential inhibitors of the individual reactions. A number of phosphorylated substrate analogues were synthesized and tested as inhibitors of D-arabinose-5-phosphate isomerase since this enzyme is the first direct reaction involved in KDO biosynthesis. (We have found no evidence that D-arabinose-5-phosphate is required in any other biosynthetic reaction in E. coli and Salmonella typhimurium it... 

Ames Test The Ames test, developed by Bruce Ames and his coworkers at the University of California, Berkeley, depends on the ability of mutagenic chemicals to bring about reverse mutations in Salmonella typhimurium strains that have defects in the histidine biosynthesis pathway. These strains will not grow in the absence of histidine but can be caused to mutate back to the wild type, which can synthesize histidine and hence can grow in its absence. The postmitochondrial supernatant (S-9 fraction), obtained from homogenates of livers of rats previously treated with PCBs in order to induce certain cytochrome P450 isoforms, is also included in order to provide the activating enzymes involved in the production of the potent electrophiles often involved in the toxicity of chemicals to animals. 

Gibbons, H.S., Lin, S., Cotter, R.J., Raetz, C.R.H. Oxygen requirement for the biosynthesis of the S-2-hydroxymyristate moiety in Salmonella typhimurium lipid A. Function of LpxO, a new Fe /alpha-ketoglutarate-dependent dioxygenase homologue. J Biol Chem 275 (2000) 32940-32949. 

Osborn, M.J. Biosynthesis and structure of the core region of lipopolysaccharide in Salmonella typhimurium. Ann N Y Acad Sci 133 (1966) 375-383. 

The bacterial reverse mutation test (Ames Test) investigates the ability of chemicals and drags to induce reverse (back) mutations in bacteria, which involves base pair substitutions additions and/or deletions (frameshift mutations) of one or a few DNA base pairs. The bacterial strains used in the test system have mutations in genes coding for enzymes required for the biosynthesis of the amino acids histidine (Salmonella typhimurium) and tryptophan (Escherichia coli). If... 

Leung, P., and Preiss, J. 1987. Biosynthesis of bacterial glycogen. Primary structure of Salmonella typhimurium ADPglucose synthetase as deduced from the nucleotide sequence of the gig C gene. J. Bacteriol. 169,4355-4360. 

Walpole CSJ, Wrigglesworth R (1987) Oxido-reductases - Flavoenzymes. In Page MI, Williams A (eds) Enzyme Mechanisms. Royal Society of Chemistry, London, p 506 Bacher A, Eberhardt S, Richter G (1996) Biosynthesis of riboflavin. In Neidhardt FC, Curtis III R, Ingraham JL, Lin ECC, Low KB, Magasanik B, Reznikoff WS, RUey M, Schaechter M, Umbarger HE (eds) Escherichia coli and Salmonella typhimurium-. Cellular and Molecular Biology.Vol 1. ASM, Washington DC,p 657... 

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