Tryptophan Salmonella typhimurium

Thicno[2,3-/ pyrrolyl)-l-alaninc 217 and 4-(6//-sclcnolo[2,3-/ pyrrolyl)-l-alanine 218, have been synthesized via reactions of thicnol 2,3-/ ]pyrrolc 215 and selenolo[2,3-fc]pyrrole 216, respectively, with 1-serine (Scheme 43). The reactions are catalyzed by Salmonella typhimurium tryptophan synthase [59,60],... 

To illustrate the use of RSSF spectroscopy to study enzyme catalysis, we give two systems detailed treatment herein, namely, horse liver alcohol dehydrogenase and Salmonella typhimurium tryptophan synthase. For an inclusive review of RSSF spectroscopy applications in the field of enzymology, see Brzovid and Dunn. ... 

Hyde, C.C., et al. Three-dimensional structure of the tryptophan synthase az pz multienzyme complex from Salmonella typhimurium. J. Biol. Chem. 263 17857-17871, 1988. 

The test is commonly employed as an initial screen for genotoxic activity and, in particular, for point mutation-inducing activity. It detects point mutations, which involve substimtion, addition or deletion of one or a few DNA base pairs. The reverse mutation test in either Salmonella typhimurium or Escherichia coli detects mutation in an amino acid requiring strain (histidine or tryptophan, respectively) to produce a strain independent of an outside supply of amino acid. The principle of the test is that it detects mutations, which revert mutations present in the test strains and restore the functional capability of the bacteria to synthesize an essential amino acid. The revertant bacteria are detected by their ability to grow in the absence of the amino acid required by the parent test strain. 

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 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... 

Ames developed strains of bacteria that had carefully selected lethal mutations. In a test system the bacteria could survive only when its mutation had been corrected by experiencing another mutation caused by the tested material. This correction could be accomplished by causing a point mutation or frameshift mutations . Point mutations are base-pair substitutions, that is, a base change in DNA of at least one DNA base pair. In a reverse mutation test, this change in base pairs may occur at the site of the original mutation, or at a secondary site in the bacterial genome. Frameshift mutations are the addition or deletion of one or more base pairs in the DNA. Since amino acids are encoded by triplets of base pairs in sequence, any addition or deletion of 1 or 2 base pairs will dramatically alter the expressed protein from that point on. The Ames system employs strains of Salmonella typhimurium and Escherichia coli that require amino acids (histidine or tryptophan, respectively) to detect such reverse point and frameshift mutations. The reverse mutation allows the S. typhimurium or E. coli strains to restore the functional capability of the bacteria to be able to synthesize the specific amino acid on their own, independent of amino acid content in the medium. 

Tryptophan synthase from Salmonella typhimurium is a symmetric a-fi-p-a complex, 15 nm in length. The X-ray structure analysis shows half of this bifunctional enzyme. 

D-form [5962-30-1] Intermediate in the biosynthesis of tryptophan in cultures of Schizophyllum commune and mutants of E. coli, Aerobacter aerogenes and Salmonella typhimurium. 2,4-Dinitrophenylhydrazone Mp 214°. 5-Phosphate Anthranilic deoxyribulotide C12H16NO9P 349.233 Intermed. in Tryptophan biosynth. 5-Phosphate, Di-Na salt.Mp 177-181°. Hygroscopic. 

Several Amadori products, notably those containing aromatic amino acid residues, have been found to behave as direct-acting mutagens in Salmonella typhimurium his strains [52] (i.e., in the Ames test), and some (e.g., nitrosated fructose-tryptophan and fructose-serotonin compounds) are known to induce DNA repair synthesis in cells of the human HeLa S3 cell line [53]. 

Negative repression was investigated in the tryptophan (trp) synthesis operons of E. coli and Salmonella typhimurium, and the histidine synthesis operon of Salmonella. The trp operon is totally derepressed in the presence of nonsurplus amounts of tryptophan. Here, transcription and translation go at maximal rates. Enzymes of the tryptophan system synthesized it in amounts which are totally utilized during translation. This condition is known as turn on. The activity of the first enzyme in the sequence of tryptophan synthesis — anthranilate synthetase — is inhibited within several seconds after the addition of surplus tryptophan. The aporepressor becomes the repressor and inhibits transcription of the operon (negative repression) after it associates with the effector, tryptophan. This association occurs if the surplus of tryptophan exists for a sufficient amount of time. After several minutes, most of the resulting mRNA is degraded and the rate of synthesis is noticeably reduced (known as the turn of condition). 

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