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Definição e significado de Tryptophan

Definição

tryptophan (n.)

1.an amino acid that occurs in proteins; is essential for growth and normal metabolism; a precursor of niacin

Tryptophan (n.)

1.(MeSH)An essential amino acid that is necessary for normal growth in infants and for NITROGEN balance in adults. It is a precursor of INDOLE ALKALOIDS in plants. It is a precursor of SEROTONIN (hence its use as an antidepressant and sleep aid). It can be a precursor to NIACIN, albeit inefficiently, in mammals.

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6-D-Tryptophan-Luteinizing Hormone-Releasing Factor (Pig) • Ardeypharm Brand of Tryptophan • Deficiency niacin(-tryptophan) • Disorders of tryptophan metabolism • ICN Brand of Tryptophan • Kalma Brand of Tryptophan • L-Tryptophan • L-Tryptophan Aminotransferase • L-Tryptophan-Related Eosinophilia-Myalgia Syndrome • L-Tryptophan-ratiopharm • Merck Brand of Tryptophan • Niddapharm Brand of Tryptophan • PMS-Tryptophan • Ratiopharm Brand of Tryptophan • Tryptophan 2,3-Dioxygenase • Tryptophan Aminotransferase • Tryptophan Decarboxylase • Tryptophan Hydroxylase • Tryptophan Indole-Lyase • Tryptophan Metabolism Alterations • Tryptophan Monooxygenase • Tryptophan Oxygenase • Tryptophan Pyrrolase • Tryptophan Synthase • Tryptophan Synthetase • Tryptophan Transaminase • Tryptophan-Specific tRNA • Tryptophan-tRNA Ligase • disorders of tryptophan metabolism • esparma Brand of Tryptophan • ratio-Tryptophan

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Tryptophan

                   
L-Tryptophan
Identifiers
CAS number 73-22-3 YesY
PubChem 6305
ChemSpider 6066 YesY
UNII 8DUH1N11BX YesY
DrugBank DB00150
KEGG D00020 YesY
ChEBI CHEBI:27897 N
ChEMBL CHEMBL54976 YesY
IUPHAR ligand 717
ATC code N06AX02
Jmol-3D images Image 1
Properties
Molecular formula C11H12N2O2
Molar mass 204.23 g mol−1
Solubility in water Soluble: 0.23 g/L at 0 °C,

11.4 g/L at 25 °C,
17.1 g/L at 50 °C,
27.95 g/L at 75 °C

Solubility Soluble in hot alcohol, alkali hydroxides; insoluble in chloroform.
Acidity (pKa) 2.38 (carboxyl), 9.39 (amino)[1]
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Tryptophan (IUPAC-IUBMB abbreviation: Trp or W; IUPAC abbreviation: L-Trp or D-Trp; sold for medical use as Tryptan)[2] is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG. Only the L-stereoisomer of tryptophan is used in structural or enzyme proteins, but the D-stereoisomer is occasionally found in naturally produced peptides (for example, the marine venom peptide contryphan).[3] The distinguishing structural characteristic of tryptophan is that it contains an indole functional group. It is an essential amino acid as demonstrated by its growth effects on rats.

Contents

  Isolation

The isolation of tryptophan was first reported by Frederick Hopkins in 1901[4] through hydrolysis of casein. From 600 grams of crude casein one obtains 4-8 grams of tryptophan.[5]

  Biosynthesis and industrial production

Plants and microorganisms commonly synthesize tryptophan from shikimic acid or anthranilate.[6] The latter condenses with phosphoribosylpyrophosphate (PRPP), generating pyrophosphate as a by-product. After ring opening of the ribose moiety and following reductive decarboxylation, indole-3-glycerinephosphate is produced, which in turn is transformed into indole. In the last step, tryptophan synthase catalyzes the formation of tryptophan from indole and the amino acid serine.

Tryptophan biosynthesis (en).svg

The industrial production of tryptophan is also biosynthetic and is based on the fermentation of serine and indole using either wild-type or genetically modified bacteria such as B. amyloliquefaciens, B. subtilis, C. glutamicum or E. coli. These strains carry either mutations that prevent the reuptake of aromatic amino acids or multiple/overexpressed trp operons. The conversion is catalyzed by the enzyme tryptophan synthase.[7]

  Function

  Metabolism of L-tryptophan into serotonin and melatonin (left) and niacin (right). Transformed functional groups after each chemical reaction are highlighted in red.

For many organisms (including humans), tryptophan is an essential amino acid. This means that it cannot be synthesized by the organism and therefore must be part of its diet. Amino acids, including tryptophan, act as building blocks in protein biosynthesis. In addition, tryptophan functions as a biochemical precursor for the following compounds (see also figure to the right):

The disorders fructose malabsorption and lactose intolerance cause improper absorption of tryptophan in the intestine, reduced levels of tryptophan in the blood[13] and depression.[14]

In bacteria that synthesize tryptophan, high cellular levels of this amino acid activate a repressor protein, which binds to the trp operon.[15] Binding of this repressor to the tryptophan operon prevents transcription of downstream DNA that codes for the enzymes involved in the biosynthesis of tryptophan. So high levels of tryptophan prevent tryptophan synthesis through a negative feedback loop and, when the cell's tryptophan levels are reduced, transcription from the trp operon resumes. The genetic organisation of the trp operon thus permits tightly regulated and rapid responses to changes in the cell's internal and external tryptophan levels.

  Dietary sources

Tryptophan is a routine constituent of most protein-based foods or dietary proteins. It is particularly plentiful in chocolate, oats, dried dates, milk, yogurt, cottage cheese, red meat, eggs, fish, poultry, sesame, chickpeas, sunflower seeds, pumpkin seeds, corn, spirulina, bananas, and peanuts.[16] Despite popular belief that turkey has a particularly high amount of tryptophan, the amount of tryptophan in turkey is typical of most poultry.[17]

Tryptophan (Trp) Content of Various Foods[17][18]
Food Protein
[g/100 g of food]
Tryptophan
[g/100 g of food]
Tryptophan/Protein [%]
egg, white, dried
81.10
1.00
1.23
spirulina, dried
57.47
0.93
1.62
cod, atlantic, dried
62.82
0.70
1.11
soybeans, raw
36.49
0.59
1.62
pumpkin seed
33.08
0.57
1.72
cheese, Parmesan
37.90
0.56
1.47
caribou
29.77
0.46
1.55
sesame seed
17.00
0.37
2.17
cheese, cheddar
24.90
0.32
1.29
sunflower seed
17.20
0.30
1.74
pistachio [19]
21.00
0.28
1.3
cashew [20]
17.00
0.25
1.47
pork, chop
19.27
0.25
1.27
turkey
21.89
0.24
1.11
chicken
20.85
0.24
1.14
beef
20.13
0.23
1.12
salmon
19.84
0.22
1.12
lamb, chop
18.33
0.21
1.17
perch, Atlantic
18.62
0.21
1.12
almond [21]
21.00
0.21
1.00
egg
12.58
0.17
1.33
wheat flour, white
10.33
0.13
1.23
baking chocolate, unsweetened
12.9
0.13
1.23
milk
3.22
0.08
2.34
rice, white
7.13
0.08
1.16
oatmeal, cooked
2.54
0.04
1.16
potatoes, russet
2.14
0.02
0.84
banana
1.03
0.01
0.87

Other herbs/plants containg tryptophan include Oenothera biennis seeds, Helianthus annuus seed, Lablab purpureus,Nasturtium officinale and Psophocarpus tetragonolobus seed and leaf.[22]

  Use as a dietary supplement and drug

There is evidence that blood tryptophan levels are unlikely to be altered by changing the diet,[23] but for some time, tryptophan has been available in health food stores as a dietary supplement.

Clinical research has shown mixed results with respect to tryptophan's effectiveness as a sleep aid, especially in normal patients.[24][25][26] Tryptophan has shown some effectiveness for treatment of a variety of other conditions typically associated with low serotonin levels in the brain.[27] In particular, tryptophan has shown some promise as an antidepressant alone[28] and as an "augmenter" of antidepressant drugs.[28][29] However, the reliability of these clinical trials has been questioned because of lack of formal controls and repeatability.[30][31][32] In addition, tryptophan itself may not be useful in the treatment of depression or other serotonin-dependent moods, but may be useful in understanding the chemical pathways that will give new research directions for pharmaceuticals.[33]

  Metabolites

A metabolite of tryptophan, 5-Hydroxytryptophan (5-HTP), has been suggested as a treatment for epilepsy[34] and depression, although clinical trials are regarded inconclusive and lacking.[35] Since 5-HTP readily crosses the blood–brain barrier and in addition is rapidly decarboxylated to serotonin (5-hydroxytryptamine or 5-HT).[36] However, serotonin has a relatively short half-life since it is rapidly metabolized by monoamine oxidase.[citation needed]

Due to the conversion of 5-HTP into serotonin by the liver, there may be a significant risk of heart valve disease from serotonin's effect on the heart.[37][38]

The primary product of the liver enzyme tryptophan dioxygenase is kynurenine.[11][39]

It is marketed in Europe for depression and other indications under the brand names Cincofarm, Tript-OH and Optimax (UK). In the United States, 5-HTP does not require a prescription, as it is covered under the Dietary Supplement Act. Since the quality of dietary supplements is now regulated by the U.S. Food and Drug Administration, manufacturers are required market products whose ingredients match the labeling, but does not establish efficacy of the product.[40]

  Tryptophan supplements and EMS

There was a large tryptophan-related outbreak of eosinophilia-myalgia syndrome (EMS) in 1989, which caused 1,500 cases of permanent disability and at least thirty-seven deaths. Some epidemiological studies[41][42][43] traced the outbreak to L-tryptophan supplied by a Japanese manufacturer, Showa Denko KK.[44] It was further hypothesized that one or more trace impurities produced during the manufacture of tryptophan may have been responsible for the EMS outbreak.[45][46] The fact that the Showa Denko facility used genetically engineered bacteria to produce L-tryptophan gave rise to speculation that genetic engineering was responsible for such impurities.[47][48] However, the methodology used in the initial epidemiological studies has been criticized.[49][50] An alternative explanation for the 1989 EMS outbreak is that large doses of tryptophan produce metabolites that inhibit the normal degradation of histamine, and excess histamine in turn has been proposed to cause EMS.[51]

Most tryptophan was banned from sale in the US in 1991, and other countries followed suit. Tryptophan from one manufacturer, of six, continued to be sold for manufacture of baby formulas. At the time of the ban, the FDA did not know, or did not indicate, that EMS was caused by a contaminated batch,[52][53] and yet, even when the contamination was discovered and the purification process fixed, the FDA maintained that L-tryptophan is unsafe. In February 2001, the FDA loosened the restrictions on marketing (though not on importation), but still expressed the following concern:

"Based on the scientific evidence that is available at the present time, we cannot determine with certainty that the occurrence of EMS in susceptible persons consuming L-tryptophan supplements derives from the content of L-tryptophan, an impurity contained in the L-tryptophan, or a combination of the two in association with other, as yet unknown, external factors."[44]

Since 2002, L-tryptophan has been sold in the U.S. in its original form. Several high-quality sources of L-tryptophan do exist, and are sold in many of the largest healthfood stores nationwide. Indeed, tryptophan has continued to be used in clinical and experimental studies employing human patients and subjects.

In recent years in the U.S., compounding pharmacies and some mail-order supplement retailers have begun selling tryptophan to the general public. Tryptophan has also remained on the market as a prescription drug (Tryptan), which some psychiatrists continue to prescribe, in particular as an augmenting agent for people unresponsive to antidepressant drugs.[citation needed]

  Turkey meat and drowsiness

A common assertion is that heavy consumption of turkey meat results in drowsiness, due to high levels of tryptophan contained in turkey.[54][55][56] However, the amount of tryptophan in turkey is comparable to that contained in most other meats.[17] Furthermore, post-meal drowsiness may have more to do with what else is consumed along with the turkey and, in particular, carbohydrates.[57] It has been demonstrated in both animal models[58] and humans[59][60][61] that ingestion of a meal rich in carbohydrates triggers release of insulin. Insulin in turn stimulates the uptake of large neutral branched-chain amino acids (BCAA), but not tryptophan (an aromatic amino acid) into muscle, increasing the ratio of tryptophan to BCAA in the blood stream. The resulting increased ratio of tryptophan to BCAA in the blood reduces competition at the large neutral amino acid transporter (which transports both BCAA and aromatic amino acids), resulting in the uptake of tryptophan across the blood–brain barrier into the cerebrospinal fluid (CSF).[62][63] Once in the CSF, tryptophan is converted into serotonin in the raphe nuclei by the normal enzymatic pathway.[58][60] The resultant serotonin is further metabolised into melatonin by the pineal gland.[10] Hence, this data suggests that "feast-induced drowsiness"— may be the result of a heavy meal rich in carbohydrates, which, via an indirect mechanism, increases the production of sleep-promoting melatonin in the brain.[58][59][60][61]

  Lifespan

Rats fed a low tryptophan diet showed reduced blood levels of triiodothyronine, which was suggested to retard the aging process.[64] Rats on tryptophan-reduced diets have shown increased maximum life span and improved biomarkers of aging (although the rate of initial deaths was higher than in controls).[65] The result was attributed to harmful effects of the age-related increase in brain serotonin. Cancers upregulate the liver enzyme tryptophan dioxygenase because its primary product, kynurenine, increases tumor growth.[39]. That would be especially relevant to lifespan studies in rodents, insofar as most rodents die of cancer[citation needed]. Additionally, excess dietary tryptophan has been shown to induce insulin resistance in pigs,[66] a physiological condition that has a deleterious effect on many organ systems.

  Fluorescence

  See also

  References

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