Histidine auxotroph

Ames test analy chem A bioassay that uses a set of histidine auxotrophic mutants of Salmomlla typhimurium for detecting mutagenic and possibly carcinogenic compounds. amz, test ... 

This assay employs a number of different strains of Salmonella typhimurium mutants that are histidine auxotrophs. The first tester strains developed and tested on extracts of diesel and ambient POM in the mid to late 1970s included TA1535, which responds to base-pair substitution chemical mutagens (e.g., /f -propiolac-tone), and TA1537 and TA1538, which respond to frameshift mutagens, e.g., BaP and other PAHs. 

The Ames Test In a nutrient medium that lacks histidine, a thin layer of agar containing 109 Salmonella ty-phimurium histidine auxotrophs (mutant cells that require histidine to survive) produces 13 colonies over a two-day incubation period at 37 °C (see Fig. 25-19). How do these colonies arise in the absence of histidine The experiment is repeated in the presence of 0.4 pg of 2-aminoanthracene. The number of colonies produced over two days exceeds 10,000. What does this indicate about 2-aminoanthracene What can you surmise about its carcinogenicity ... 

Humans have used fire for cooking since about 105 years ago. The presence of polycyclic aromatic hydrocarbons in broiled foods such as beefsteak and broiled fish has been reported (1, 2). The presence of genotoxic substances in broiled foods other than typical carcinogenic hydrocarbons was detected after the development of Ames Salmonella/mammalian-microsome test (3). Charred parts of broiled fish and meat showed mutagenicity towards Salmonella typhirmcrium TA98, a fraraeshift mutant of histidine auxotroph, in the presence of S9 mix, a mixture of rat liver... 

Geiger LE, Neal RA. 1981. Mutagenicity testing of 2,3,7,8-tetrachlorodibenzo-p-dioxin in histidine auxotrophs of Salmonella typhimurium. Toxicol Appl Pharmacol 59 125-129. 

The Ames test utilizes several different histidine auxotrophic mutants... 

Prokaryotic organisms Salmonella typhimurium (histidine auxotrophs) Gene mutation + - Simmon and Shepherd 1978a... 

A recent X-ray work (87) on a-lytic protease showed that Asp-102 is in a strongly polar environment with a pK of 4.5. Furthermore, histidine, enriched in in the imidazole ring, has been incorporated into a-lytic protease, using a histidine auxotroph of Myxobacter 495 (88). The behavior of the N-NMR resonances of this labeled a-lytic protease in the catalytic triad as a function of pH indicated clearly the presence of a hydrogen-bonded interaction between NH at the position-3 of histidine (N51) and the adjacent buried carboxylate group of aspartic acid. 

Studies with histidine auxotrophs of Salmonella typhimurium showed that mixing extracts of a strain unable to produce compound III with that of a strain capable of producing III, but unable to convert it to the aminoribosylimidazolecarboxamide phosphate and imidazoleglycerol phosphate, carried the reaction to completion with the formation of both of these compounds. 

Puromycin also revealed differential inhibitory effects on the synthesis of the individual outer membrane proteins (Table I). The synthesis of peak 11 protein was found to be strikingly more resistant to puromycin than that of the other outer membrane proteins. Since puromycin is known to inhibit protein synthesis by prematurely terminating peptide formation, it is important to rule out the possibility that the appearance of peak 11 formed in the presence of puromycin may be due to the prematurely terminated peptides of other envelope proteins which have a size coincident with that of peak 11 protein and can still be incorporated into the membrane. As will be discussed in more detail later, this protein is a lipoprotein and can be specifically labeled with radioactive palmitic acid. Furthermore, since the lipoprotein does not contain any histidine residues, it can be normally synthesized even in a histidine auxotroph of E. coli which is being starved... 

One interesting approach for probing the assembly mechanism of the lipoprotein is to study the exclusive biosynthesis of the lipoprotein in vivo. Since this protein has no histidine, it is the only envelope protein synthesized in the absence of histidine in an E. coli histidine auxotroph as discussed earlier (3.1). As shown in Fig. 11, in the absence of histidine,... 

Fig. 11. Gel electrophoresis of the envelope fractions of an E. coli histidine auxotroph ( . coli CP78) labeled with [ C]arginine in the presence and absence of histidine. (A) Labeled in the presence of histidine for 1 h. (B) Labeled during a 1-h histidine starvation. (C) Labeled for 2 h after 2 h of histidine starvation. The patterns of the envelope fractions with and without the lysozyme treatment were superimposed with the aid of the internal standards. Envelope fractions treated with T4 phage lysozyme ------- without T4 phage treatment . In the case of...

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