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coli, tryptophan biosynthesis in
If a metabolic pathway branches, leading to the synthesis of twoaminoacids, each end product (amino acid) can control its own synthesiswithoutaffecting the other (Figure 4). For example, the amino acids prolineandarginine are both synthesized from glutamic acid. Each amino acid canregulatethe first enzyme unique to its own synthesis without affecting theother,so that a surplus of arginine will not shut off the synthesisof proline and vice versa.
This observation suggests that E4P, for tryptophan biosynthesis, is provided by the linkage between the intermediates of glycolysis, fructose-6-phosphate and glyceraldehyde-3-phosphate, through the activity of the transketolases and transaldolases of the nonoxidative steps of the HMP.
Escherichia coli K-12 substr. MG1655 L-tryptophan biosynthesis
It was found that erythrose-4-phosphate (E4P), a precursor to aromatic amino acid biosynthesis, is produced by the non-oxidative portion of the hexose monophosphate pathway, since it lacks 6-phosphogluconate dehydrogenase.
Metabolism1.0 Global and overview maps1.1 Carbohydrate metabolism1.2 Energy metabolism1.3 Lipid metabolism1.4 Nucleotide metabolism1.5 Amino acid metabolism1.6 Metabolism of other amino acids1.7 Glycan biosynthesis and metabolism1.8 Metabolism of cofactors and vitamins1.9 Metabolism of terpenoids and polyketides1.10 Biosynthesis of other secondary metabolites1.11 Xenobiotics biodegradation and metabolism1.12 Chemical structure transformation maps
Biosynthetic Manipulation of Tryptophan in ..
L-tryptophan (L-Trp) is a fundamental precursor of various neurotransmitters in the brain, which are essential for the regulation of mood, sleep, appetite and pain level, such as melatonin, niacin and serotonin (-). It is used widespread in the pharmaceutical industry for the chemical synthesis of a range of drugs such as antidepressants, sedative pharmaceuticals and drugs used for the treatment of schizophrenia and alcoholism (, ). It is also used as a food supplement in animal feeds (). There are chemical and microbial processes for L-Trp production. All chemical synthesis yield DL-Tryptophan and the product must be resolved for the separation of the biologically active L-isomer (). The majority of L-Trp production depends on microbial processes. These processes include direct fermentation from carbohydrates or hydrocarbons, enzymatic reaction from L-Trp precursors and bioconversion from L-Trp precursors. Effective production processes are available with mutants of Escherichia coli (), Corynebacterium glutamicum (), Bacillus subtilis () and Brevibacterium lactofermentum ().
Although, many industrial processes employ E. coli cells which have L-tryptophan synthase (TSase, EC 18.104.22.168) activity to convert indole and L-serine (L-Ser) to L-Trp (); since this type of production is based on a very simple and one-step reaction therefore the complete biosynthetic pathway of L-Trp isn’t necessary and the complicated mutations of microorganisms which control the regulatory mechanisms are often not required (). However, there are disadvantages to these processes because precursors are expensive. Indole is available from the petrochemical industry as a comparably inexpensive educt, whereas L-Ser is very expensive because a racemic mixture is formed during its manufacture. To address this problem, new methods for both process design and cheap precursor substitution have been developed, for example production of L-Ser from methanol and glycine by methanol-utilizing bacteria (-). Recovery of L-Ser from the by-products of various industries provides another means that may be more efficient than the latter.
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trpC - Tryptophan biosynthesis protein TrpCF - …
Feedback inhibition (or end product inhibition) is amechanismfor the inhibition of preformed enzymes that is seen primarilyinthe regulation of whole biosynthetic pathways, e.g. pathways involvedinthe synthesis of the amino acids. Such pathways usually involve manyenzymaticsteps, and the final (end) product is many steps removed from thestartingsubstrate. By this mechanism, the final product is able to feed back tothe first step in the pathway and to regulate its own biosynthesis.
Logic for regulating tryptophan biosynthesis
In feedback inhibition, the end product of a biosynthetic pathwayinhibitsthe activity of the first enzyme that is unique to the pathway, thuscontrollingproduction of the end product. The first enzyme in the pathway is anallostericenzyme. Its allosteric site will bind to the end product (e.g. aminoacid)of the pathway which alters its active site so that it cannot mediatetheenzymatic reaction which initiates the pathway. Other enzymes in thepathwayremain active, but they do not see their substrates. The pathway isshutdown as long as adequate amounts of the end product are present. If theend product is used up or disappears, the inhibition is relieved, theenzymeregains its activity, and the organism can resume synthesis of the endproduct. Thus, if a bacterium swims out of a glucose minimal mediuminto milk or some other medium rich in growth factors, the bacteriumcanstop synthesizing any of the essential metabolites that are madeavailabledirectly from the new environment.
Complexity in Regulation of Tryptophan Biosynthesis in ..
L-tryptophan is an important ingredient in medicines, especially in neuromedicines such as antidepressants. Many commercial processes employ various microorganisms with high tryptophan synthase activity to produce L-tryptophan from indole and L-serine, but these processes are very costly due to the costs of precursors, especially L-serine.
crucial to regulation of tryptophan biosynthesis ..
Whole cells of Escherichia coliATCC 11303 were induced for L-tryptophan synthase by addition of indole to the growth medium and bacterial cells harvested from the growth medium were used as biocatalysts in the production medium. Conditions of the production medium were optimized and Iranian cane and beet molasses were processed by solvent extraction with ethanol and n-butanol and used as L-serine sources of the production medium. Amount of L-tryptophan and theoretical yield of L-tryptophan production were determined by High Performance Liquid Chromatography and by a colorimetrical method on the basis of the remaining indole assay, respectively.
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