Tryptophanes, synthesis

A versatile tryptophan synthesis which proceeds directly from indoles as starting materials was developed by Gilchrist[5], The alkylation reagent is the... 

In the course of their investigation of the enantioselective total synthesis of avarainvillamide and the stephacidins, the Baran group has developed a method for the dehydrogenation of tryptophan as well as a one-step tryptophan synthesis from pyroglutamate and substituted aniline precursors <06JACS8678>. 

From this point on there are numerous ways of proceeding with the analysis. Crude extracts can be made from different mutant cells. The extract from one mutant can be used to complement the extract from another mutant in tryptophan synthesis, which can lead to an assay for a particular enzyme carried by one mutant that is missing in the other mutant. The goal at this juncture is to purify each enzyme of the pathway so that the properties of the enzymes and the reactions they catalyze can be individually scrutinized. All of the tryptophan enzymes have been isolated from E. coli. Studies of other systems indicate a remarkable similarity for the operation of this pathway in different microorganisms and plants. 

Among different organisms the five enzyme activities required for tryptophan synthesis are distributed on different proteins (table 21.1). For example, in E. coli, indoleglycerol phosphate synthase catalyzes both the isomerization of phosphoribosylanthranilate and the cyclization step. Of particular interest is the occurrence of a single protein of the catalytic activities for nonconsecutive reactions in some cases. If in such cases the proteins were separate from each other in the cell, this arrangement, for example, in Neurospora, would necessitate the product of one reaction leaving the product site of one enzyme to be acted on by another... 

When tryptophan is lacking, a trp repressor protein (encoded by the trpR operon) is synthesized. The trp repressor dimer is inactive, cannot bind to the trp operator and so the trp operon is transcribed to produce the enzymes that then synthesize tryptophan for the cell. When tryptophan is present, tryptophan synthesis is not needed. In this situation, acting as a corepressor, tryptophan binds to the repressor and activates it so that the repressor now binds to the trp operator and stops transcription of the trp operon. 

We noted earlier the coordinate repression of the enzymes for tryptophan synthesis in the presence of tryptophan. When the level of tryptophan is depleted or reduced, trp mRNA is synthesized in 3-4 minutes and rapidly degraded it has a half-life of some 3 minutes. This allows the bacteria to respond quickly to changing requirements for tryptophan. 

Partridge and co-workers (663) showed that such a cycle plays no part under conditions of normal tryptophan synthesis, and Adelberg (4) has plausibly ascribed the original results to adaptive formation of the enzyme kynureninase (discussed in detail later) induced by the high tryptophan content of the medium. 

In studying the biochemical genetics of tryptophan synthesis in Pseudomonas acidovorans, Buvinger et al.6 isolated 60 independent tryptophan auxotrophs of Pseudomonas acidovorans and characterized them for nutritional response to intermediates of the pathway, accumulation of intermediates, and levels of tryptophan-synthetic enzymes. Mutants for each of the seven proteins catalyzing the five steps of tryptophan synthesis were... 

In order to prove that regulation by attenuation occurs in vivo, Charles Yanofsky and others studied tryptophan synthesis regulation in a series of E. colt mutants. For each mutant described below predict the expression of tryptophan synthesis genes in the presence or absence of tryptophan. 

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