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06.05.2012.

Essential amino-acids


Amino acids are molecules containing an amine group, a carboxylic acid group, and a side-chain that is specific to each amino acid. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen. They are particularly important in biochemistry, where the term usually refers to alpha-amino acids.



There are essential and non-essential amino-acids.
An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized by the organism (usually referring to humans), and therefore must be supplied in the diet.


Essential amino-acids
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
Histidine

The amino acids regarded as essential for humans are phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, leucine, lysine, and histidine. Additionally, cysteine (or sulphur-containing amino acids), tyrosine (or aromatic amino acids), and arginine are required by infants and growing children. Essential amino acids are "essential" not because they are more important to life than the others, but because the body does not synthesize them, making it essential to include them in one's diet in order to obtain them. In addition, the amino acids arginine, cysteine, glycine, glutamine, histidine, proline, serine and tyrosine are considered conditionally essential, meaning they are not normally required in the diet, but must be supplied exogenously to specific populations that do not synthesize it in adequate amounts.

Isoleucine

Isoleucine (abbreviated as Ile or I) is an α-amino acid with the chemical formula HO2CCH(NH2)CH(CH3)CH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested.



Even though this amino acid is not produced in animals, it is stored in high quantities. Foods that have high amounts of isoleucine include eggs, soy protein, seaweed, turkey, chicken, lamb, cheese, and fish.

Leucine

Leucine (abbreviated as Leu or L) is a branched-chain α-amino acid with the chemical formula HO2CCH(NH2)CH2CH(CH3)2.



Food
g/100g
Soy protein concentrate
4.917
Soybeans, mature seeds, raw
2.97
Beef, round, top round, separable lean and fat
1.76
Peanuts
1.672
Salami, Italian, pork
1.63
Fish, salmon, pink, raw
1.62
Wheat germ
1.571
Almonds
1.488
Chicken, broilers or fryers, thigh, meat only, raw
1.48
Chicken egg, yolk, raw, fresh
1.40
Oat
1.284
Beans, pinto, cooked
0.765
Lentils, cooked
0.654
Chickpea, cooked
0.631
Corn, yellow
0.348
Cow milk, whole, 3,25% fat
0.27
Rice, brown, medium-grain, cooked
0.191
Milk, human, mature, fluid
0.10

Lysine

Lysine (abbreviated as Lys or K) is an α-amino acid with the chemical formula HO2CCH(NH2)(CH2)4NH2. It is an essential amino acid, which means that the human body cannot synthesize it.



The nutritional requirement per day, in milligrams of lysine per kilogram of body weight, is: infants (3–4 months) 103, children (2 years) 64, older children (10–12 years) 60 to 44, adults 12. For a 70 kg adult, 12 milligrams of lysine per kilogram of body weight is 0.84 grams of lysine. Good sources of lysine are foods rich in protein such as soy, as well as meat (specifically red meat, lamb, pork, and poultry), cheese (particularly Parmesan), certain fish (such as cod and sardines), and eggs.
Lysine is the limiting amino acid (the essential amino acid found in the smallest quantity in the particular foodstuff) in most cereal grains, but is plentiful in most pulses (legumes). Consequently, meals that combine cereal grains and legumes, such as the Indian dal with rice, Middle Eastern hummus, ful medames, falafelpita bread, the Mexican beans with rice or tortilla have arisen to provide complete protein in diets that are, by choice or by necessity, vegetarian. with A food is considered to have sufficient lysine if it has at least 51 mg of lysine per gram of protein (so that the protein is 5.1% lysine).
Foods containing significant amounts of lysine include:
  • Catfish, channel, farmed, raw: 9.19% of the protein is lysine.
  • Chicken, roasting, meat and skin, cooked, roasted: 8.11% of the protein is lysine.
  • Beef, ground, 90% lean/10% fat, cooked: 8.31% of the protein is lysine.
  • Soybean, mature seeds, raw: 7.42% of the protein is lysine.
  • Soybean, mature seeds, sprouts: 5.74% of the protein is lysine (sprouting decreases the lysine content).
  • Winged Bean (aka Goa Bean or Asparagus Pea), mature seeds, raw: 7.20% of the protein is lysine.
  • Lentil, pink, raw: 6.97% of the protein is lysine.
  • Lentil, sprouts, raw: 7.95% of the protein is lysine (sprouting increases the lysine content).
  • Parmesan cheese, grated: 7.75% of the protein is lysine.
  • Azuki bean (adzuki beans), mature seeds, raw: 7.53% of the protein is lysine.
  • Milk, non-fat: 7.48% of the protein is lysine.
  • Egg (food), whole, raw: 7.27% of the protein is lysine.
  • Pea, split, mature seeds, raw: 7.22% of the protein is lysine.
  • Kidney Bean, mature seeds, raw: 6.87% of the protein is lysine.
  • Chickpea, (garbanzo beans, Bengal gram), mature seeds, raw: 6.69% of the protein is lysine.
  • Navy Bean, mature seeds, raw: 5.73% of the protein is lysine.
  • Amaranth, grain, uncooked: 5.17% of the protein is lysine.

Methionine

Methionine (abbreviated as Met or M) is an α-amino acid with the chemical formula HO2CCH(NH2)CH2CH2SCH3. This essential amino acid is classified as nonpolar.



High levels of methionine can be found in eggs, sesame seeds, Brazil nuts, fish, meats and some other plant seeds; methionine is also found in cereal grains. Most fruits and vegetables contain very little of it. Most legumes are also low in methionine. The complement of cereal (methionine) and legumes (lysine), providing a complete protein is a classic combination, found throughout the world, such as in rice and beans or tortilla and beans.
Racemic methionine is sometimes added as an ingredient to pet foods.

Food
g/100g
Egg, white, dried, powder, glucose reduced
3.204
Sesame seeds flour(low fat)
1.656
Egg, whole, dried
1.477
Cheese, parmesan, shreeded
1.114
Brazil nuts
1.008
Soy protein concentrate
0.814
Chicken, broilers or fryers, roasted
0.801
Fish, tuna, light, canned in water, drained solids
0.755
Beef, cured, dried
0.749
Bacon
0.593
Beef, ground, 95% lean meat/ 5% fat, raw
0.565
Pork, ground, 96% lean/ 4% fat, raw
0.564
Wheat germ
0.456
Oat
0.312
Peanut
0.309
Chickpea
0.253
Corn, yellow
0.197
Almonds
0.151
Beans, pinto, cooked
0.117
Lentils, cooked
0.077
Rice, brown, medium-grain, cooked
0.052

Phenylalanine

Phenylalanine (abbreviated as Phe or F) is an α-amino acid with the formula C6H5CH2CH(NH2)COOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain.



Phenylalanine is found naturally in the breast milk of mammals. It is used in the manufacture of food and drink products and sold as a nutritional supplement for its reputed analgesic and antidepressant effects. It is a direct precursor to the neuromodulator phenylethylamine, a commonly used dietary supplement.

Threonine

Threonine (abbreviated as Thr or T) is an α-amino acid with the chemical formula HO2CCH(NH2)CH(OH)CH3.



Foods high in threonine include cottage cheese, poultry, fish, meat, lentils, and sesame seeds.

Tryptophan

Tryptophan (IUPAC-IUBMB abbreviation: Trp or W; IUPAC abbreviation: L-Trp or D-Trp; sold for medical use as Tryptan) is one of the 20 standard amino acids, as well as an essential amino acid in the human diet.
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):
  • Serotonin (a neurotransmitter), synthesized via tryptophan hydroxylase. Serotonin, in turn, can be converted to melatonin (a neurohormone), via N-acetyltransferase and 5-hydroxyindole-O-methyltransferase activities.
  • Niacin is synthesized from tryptophan via kynurenine and quinolinic acids as key biosynthetic intermediates.
  • Auxin (a phytohormone) when sieve tube elements undergo apoptosis tryptophan is converted to auxins. 


 
Food
Protein(g/100g)
Tryptophan(g/100g)
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
21.00
0.28
1.30
Cashew
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
21.00
0.21
1.00
Egg
12.58
0.17
1.33
Wheat flour, white
10.33
0.13
1.23
Baking chocolate, unsweetened
12.90
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

The disorders fructose malabsorption and lactose intolerance cause improper absorption of tryptophan in the intestine, reduced levels of tryptophan in the blood and depression.
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. Despite popular belief that turkey has a particularly high amount of tryptophan, the amount of tryptophan in turkey is typical of most poultry.

Valine

Valine (abbreviated as Val or V) is an α-amino acid with the chemical formula HO2CCH(NH2)CH(CH3)2.



Along with leucine and isoleucine, valine is a branched-chain amino acid. It is named after the plant valerian. In sickle-cell disease, valine substitutes for the hydrophilic amino acid glutamic acid in hemoglobin. Because valine is hydrophobic, the hemoglobin is prone to abnormal aggregation.
Valine is an essential amino acid, hence it must be ingested, usually as a component of proteins. It is synthesized in plants via several steps starting from pyruvic acid. The initial part of the pathway also leads to leucine.




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