Arginine | Introduction | History | Applications....

 Arginine | Introduction | History | Applications....

ARGININE AMINO ACID

                             

Introduction-

Arginine, also known as l-arginine is an essential α-amino acid. It is used in the biosynthesis of proteins.  It contains an α-amino group and α-carboxylic acid group.  A side chain consisting of a 3-carbon aliphatic straight chain ending in a guanidine group.  At physiological pH, the carboxylic acid is deprotonated (−COO⁻), the amino group is protonated (−NH₃⁺).  The guanidino group is also protonated to give the guanidinium form (-C-(NH₂)₂⁺).  It is the precursor for the biosynthesis of nitric oxide. It is encoded by the codons CGU, CGC, CGA, CGG, AGA, and AGG.

Arginine is classified as a semiessential or conditionally essential amino acid. Preterm infants are unable to synthesize or create arginine internally, making the amino acid nutritionally essential for them.  Most healthy people do not need to supplement with arginine because it is a component of all protein-containing food  and can be synthesized in the body from glutamine via citrulline.

Properties-

Chemical formula :- C₆H₁₄N₄O₂

Molar mass :- 174.204 g·mol−1

Appearance :- White crystals

Odor :- Odourless

Melting point :- 260 °C; 500 °F; 533 K

Boiling point :- 368 °C (694 °F; 641 K)

Thermodynamic data :- Phase behaviour (solid–liquid–gas)

Structure- 

                         

History-

Arginine was first discovered in 1886 from yellow lupin seedlings by the German chemist Ernst Schulze  and his assistant Ernst Steiger. He named it from the "silver" due to the silver-white appearance of arginine nitrate crystals. In 1897, Schulze and Ernst Winterstein (1865–1949) determined the structure of arginine. Schulze and Winterstein synthesized arginine from ornithine and cyanamide in 1899.

Sources-

Dietary sources-

Arginine is a conditionally essential amino acid in humans and rodents. It may be required depending on the health status or lifecycle of the individual. When the small intestine and kidneys which are the major sites of arginine biosynthesis, have been damaged.

Animal sources of arginine include meat, dairy products, and eggs and plant sources include seeds of all types, for example grains, beans, and nuts.

Biosynthesis-

Arginine is synthesized from citrulline in arginine and proline metabolism by the sequential action of the cytosolic enzymes argininosuccinate synthetase and argininosuccinate lyase. This is an energetically costly process, because for each molecule of argininosuccinate that is synthesized, one molecule of adenosine triphosphate (ATP) is hydrolyzed to adenosine monophosphate (AMP), consuming two ATP equivalents.

Citrulline can be derived from multiple sources.

Arginine biosynthesis-

Whole-body basis, synthesis of arginine occurs principally via the intestinal–renal axis. The epithelial cells of the small intestine produce citrulline, primarily from glutamine and glutamate. which is carried in the bloodstream to the proximal tubule cells of the kidney, which extract citrulline from the circulation and convert it to arginine, which is returned to the circulation.

Structure- The amino acid side-chain of arginine consists of a 3-carbon aliphatic straight chain, the distal end of which is capped by a guanidinium group, which has a pk, of 12.48, and is therefore always protonated and positively charged at physiological pH. Because of the conjugation between the double bond and the nitrogen lone pairs, the positive charge is delocalized, enabling the formation of multiple hydrogen bonds.

Function-

Arginine participates in a number of metabolic pathways depending on the cell type.

 It is synthesized as an intermediate in the urea cycle pathway.

It is also obtained from dietary proteins.

 A number of key metabolites such as nitric oxide, phosphocreatine, spermine, and ornithine are derived from arginine.

Arginine is important for promoting immune system function.

 It also serves as a precursor for nitric oxide (NO), polyamines, and creatine.

 It may also activate the mammalian target of rapamycin (mTOR) signaling pathway in the small intestines, which plays a major role in cell growth and proliferation.

 

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