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Proteins are made up of one or more polypeptide molecules which are formed by amino acids. During the formation of polypeptide molecules, amino acids are linked covalently by an amide linkage which called as peptide bonds.

Each polypeptide chain contains two terminals one is known as amino terminal or N-terminal with a free amino group and another is a carboxyl group, known as carboxyl terminal or C-terminal. N-terminal is written at the upper left and the C-terminal at the lower right in polypeptide chain. This sequence of amino acids in proteins is known as primary structure of proteins.

The orientation of polypeptide chain in protein makes different levels of proteins. The formation of secondary hydrogen bonds between the oxygen atom of one amino acid and the nitrogen atom of another amino acid arranged the polypeptide chains in two dimensional space which gives the secondary structure of proteins.
It can be two types, a beta-pleated sheet or alpha-helix.

The folding of long chains of amino acids in three dimensional gives the tertiary structure of proteins. Folding of chain gets stabilized by various interactions like ionic bonds, hydrogen bonds, covalent bonds and hydrophobic interactions. Some proteins like antibody molecules and hemoglobin, several polypeptides can bonded together to form a quaternary structure.


What is Arginine?

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Arginine is an essential amino acid which has a positively charged guanidino group in side chain of molecule. Arginine amino acid has capability to bind with the phosphate anion and also acts as the active centers of proteins which bind phosphorylated substrates.
Arginine plays an important role in maintaining the overall charge balance of a protein and in nitrogen metabolism. In the urea cycle, Arginine gets decompose to urea and the L-amino acid Ornithine in the presence of arginase enzyme. There are six codons in the genetic code for Arginine; CGC, CGG, CGA, AGG, AGA, and CGU.
Arginine is an essential amino acid involves in cell division and protein synthesis, thus must be obtained from the diet. Arginine intake is wide to take during the periods of growth like in childhood and pregnancy, when body is actively use amino acid for protein synthesis. Although there are many Arginine supplements are available in the market, yet the natural ways of obtaining Arginine is the best way. There are many food sources of Arginine amino acid.

Some of them are as follow.

a) Nuts: Plant products like nuts are the richest sources of Arginine which contains around 1 to 3 g per 100 g of nuts. Some nuts with their argenine content are as follow.
  • Peanuts -3.1 g per 100 g
  • Almonds -2.5 g per 100 g
  • Walnuts -2.3 g per 100 g
  • Hazelnuts -2.2 g per 100 g
  • Cashews -2.1 g per 100 g
  • Pistachios -2.03 g per 100 g
  • Brazil nuts -2.15 g per 100 g
  • Pecans -1.18 g per 100 g
b) Spinach and Lentils: Vegetables are very good sources of protein, particularly they have a concentration of Arginine. Spinach and lentils are most common vegetables rich in Arginine content. Frozen spinach contain 3.3 g of arginine per 100 g and lentils have 2.1 g per 100 g of the raw vegetable.
Some other vegetable sources of Arginine are as follow.
  • Flax seed -1.93 g
  • Raw kidney beans -1.46 g
  • Raw French beans -1.17 g
  • Raw green soybeans -1.04 g
  • Raw garlic -0.63 g
  • Blueberry muffins -0.30 g
  • Raw onion -0.10 g
c) Whole Grains: Cereal grains like whole wheat contains the highest content of arginine, around 650 mg per 100 g. Hence breads and pastas made from whole grain are rich in arginine.

d) Soya: Soya-based proteins contain a high content of arginine.100 g of tofu contains 600 mg of Arginine and a 200 calorie serving from soy proteins isolate has more than 4 g of Arginine.

e) Seafood: Sea food like crustaceans is the best animal-based sources of arginine. A 200-calorie serving of food like crabs, shrimps or lobsters contains 3.6 to 3.8 g of arginine. Tuna and salmon fishes contain maximum amount of arginine 1.7 g per 100 g and 1.2 g per 100 g respectively. Chicken and pork have even greater amount of Arginine compare to sea food.

f) Eggs: The yolk part of eggs is very rich in this amino acid. Around 1.10 g of argenine present in 100 g of raw egg yolk while 0.65 g per 100 g is in raw egg white. Some other food sources with Arginine content are as follows.
Food items Arginine content (g/100 g edible portion)
1 Seeds, sesame flour, low-fat 7.44
2 Seeds, cottonseed flour, low fat (glandless) 6.73
4 Soy protein isolate, potassium type 6.67
5 Soy protein isolate 6.67
6 Seeds, cottonseed meal, partially defatted (glandless) 6.63
7 Gelatins, dry powder, unsweetened 6.62
8 Soy protein isolate, PROTEIN TECHNOLOGIES INTERNATIONAL, ProPlus 6.50
9 Peanut flour, defatted 6.24
10 Seeds, sesame flour, partially defatted 5.98
11 Seeds, cottonseed flour, partially defatted (glandless) 5.53
12 Seeds, pumpkin and squash seed kernels, roasted, with salt added 5.42
13 Seeds, sunflower seed flour, partially defatted 5.70
14 Mollusks, whelk, unspecified, cooked, moist heat 4.94
15 Seeds, watermelon seed kernels, dried 4.90
16 Nuts, butternuts, dried 4.86
17 Snacks, pork skins, plain 4.84
18 Egg, white, dried, powder, glucose reduced 4.81

Arginine Structure

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The IUPAC name of Arginine is 2-Amino-5-guanidinopentanoic acid with molecular formula C6H14N4O2 and molecular mass is 174.2 g/mol. The side chain of Arginine composed of three carbon atoms of aliphatic straight chain which is capped by a complex guanidinium group.

Arginine Structure

Because of the presence of positively charged guanidinium group in side chain, Arginine is a most basic, positive charged amino acid. The isoelectric point of Arginine has high pH value due to the extra positive charge on side chain.

Hence, pI = 1/2 ($pK_{a2}$ + $pK_{a3}$), for Arginine; $pK_{a1}$=2.2($\alpha $-COOH group), $pK_{a2}$=9.0 ($\alpha $-NH2 group) and $pK_{a3}$=12.5 (forguanidinium group).

Therefore, the isoelectric point of Arginine is 10.76.

Isoelectric Point of Arginine

The titration curve of Arginine show three inflection points related to different form of zwitter ions. The very high concentration of hydroxyl ion required to remove the last acidic proton from Arginine shows that the exceptionally high basicity of the guanidine group of amino acid.

Titration Curve of Arginine

Like other amino acids; Arginine also exists in D and L configurations which are differing in orientation of amino and carboxyl group.

                                      D and L configuration of Arginine

Arginine Nitrate

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The oxidation of argenine to nitric oxide is catalyzed by nitric oxide synthase (eNOS) during Nitrate-nitrite-nitric oxide formation/recycle pathways.

The product, nitric oxide (NO) can show various biological effects and increase the tissue perfusion along with angio- and arteriogenosis in PAD models. Nitric oxide is rapidly oxidized to nitrite ion NO2- and nitrate ion NO3-.

Arginine Nitrate

Nitric oxide NO is well known for its vasoregulatory properties and used for the therapeutic treatment due to its vasoprotective abilities. L-Arginine involve in biosynthesis of nitric oxide catalysed by a group of enzymes commonly called as nitric oxide synthases (NOSs).

The overall reaction is as follow.

L-arginine + $\frac{3}{2}$NADPH + H+ + 2O2 $\to $ citrulline + nitric oxide + $\frac{3}{2}$NADP+

This conversion is also known as L-arginine-nitric oxide (NO) pathway which play an important role during transplant rejection, organ injury, infection, and, inflammation.

Hence, Arginine nitrate is the latest ingredients of workout supplements which are mainly part of the nitric oxide family and helps body by injecting a shot of nitric oxide into muscles and bloodstream during workout. Two common trademark of Arginine nitrate are Yok3d and NO3 Chrome.

Arginine Nitrate is also work in the same manner as L-Arginine and helps to drive nitric oxide into muscles and bloodstream to promote the nutrient delivery and gives pumps by "reverse nitric oxide pathway". Arginine Nitrate shows very less side Effects. A very less number of patients have experienced some complains like diarrhea and bloating.

Benefits of Arginine

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Out of D and L-arginine, L-arginine involves in various biochemical reactions and help in treatment of illnesses and disorders which improve blood vessels relax. L-arginine is also used for the treatment of chest pain, erectile dysfunction, coronary artery disease, clogged arteries, peripheral vascular disease, vascular headaches and congestive heart failure.

It is also found helpful in the healing of wounds an inhibiting the wasting process in patients with critical illnesses.

Some other benefits of Arginine are as follows.
  1. L-arginine acts as a precursor of nitric oxide and other biochemical compounds, enzymes and hormones like vasopressin, skin and connective tissues and also involves in regulation of platelet aggregation and lowering of blood pressure. It plays important roles in the synthesis of various protein molecules like creatine and insulin.
  2. L-arginine is converted to nitric oxide, which improved blood circulation in the body. L-arginine helps in stimulating and maintaining penile erection as it is a major component of ejaculate, hence it is important for maintaining healthy ejaculate volume.
  3. L-arginine helps to remove the excess ammonia and maintain the nitrogen balance. It is helpful for reduction of accumulation of by products of physical exercise like ammonia and plasma lactate and also helps in reduction of alcohol toxicity effects, wound healing and liver detoxification.
  4. Deficiency of arginine is responsible for the delay of glucose tolerance, liver lipid metabolism, sexual maturity and impairment of the production of insulin.
  5. Arginine converts into nitric oxide (NO) which is a powerful neurotransmitter and helpful in blood vessels relaxation and also improves circulation.

Arginine can improve the blood flow in the arteries of the heart and improve symptoms of coronary artery disease, chest pain, clogged arteries and angina. Arginine includes in helping the kidneys remove waste products from the body and maintaining immune and hormone function. Some more benefits of Arginine amino acid are as follows.
  • Body building, muscle growth.
  • Helpful in the treatment of Cancer or tumors.
  • Helpful in exercise and athletic performance.
  • Used to increase the level of growth hormones.
  • Good for heart disease.
  • Help in improvement of heart transplant patients.
  • Help in reducing the hypertension and high blood pressure.
  • Beneficial for the gestational hypertension and proteinuria
  • Improves the hemodynamic responses to stress and reduces plasma homo cysteine.
  • Affected the hemodynamic, glucose, insulin, or C-reactive protein.
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