''N''-Acetylglutamic acid (also referred to as ''N''-acetylglutamate, abbreviated NAG, chemical formula C₇H₁₁NO₅) is biosynthesized from

glutamate Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a Essential amino acid, non-essential nutrient for humans, meaning that ...

and acetylornithine by ornithine acetyltransferase, and from

glutamic acid Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α- amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can ...

and

acetyl-CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidation, o ...

by the enzyme ''N''-acetylglutamate synthase. The reverse reaction, hydrolysis of the acetyl group, is catalyzed by a specific

hydrolase In biochemistry, hydrolases constitute a class of enzymes that commonly function as biochemical catalysts that use water to break a chemical bond: :\ce \quad \xrightarrowtext\quad \ce This typically results in dividing a larger molecule into s ...

. It is the first intermediate involved in the biosynthesis of

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...

in prokaryotes and simple eukaryotes and a regulator in the process known as the

urea cycle The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea (NH2)2CO from ammonia (NH3). Animals that use this cycle, mainly amphibians and mammals, are called ureotelic. The urea cycle converts highl ...

that converts toxic ammonia to urea for excretion from the body in vertebrates.

Discovery

''N''-Acetylglutamic acid is an extracellular

metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...

isolated from the prokaryote

Rhizobium ''Rhizobium'' is a genus of Gram-negative soil bacteria that fix nitrogen. ''Rhizobium'' species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. The bacteria colonize plant ce ...

trifolii that was characterized using many structure determination techniques such as proton nuclear magnetic resonance (¹H NMR) spectroscopy, Fourier-transform infrared spectroscopy, and gas chromatography-mass spectrometry. In ''

'', extracellular build-up of ''N''-acetylglutamic acid is due to metabolism involving nod factor genes on a

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria and ...

. When the nod factors are mutated, less ''N''-acetylglutamic acid is produced.

Biosynthesis

Prokaryotes and simple eukaryotes

In prokaryotes and simple eukaryotes, ''N''-acetylglutamic acid can be produced by ''N''-acetylglutamate synthase (NAGS) or ornithine acetyltransferase (OAT).

Ornithine acetyltransferase (OAT) synthesis

OAT synthesizes ''N''-acetylglutamic acid from

and acetylornithine and is the method of choice for production in prokaryotes that have the ability to synthesize the compound

ornithine Ornithine is a non-proteinogenic α-amino acid that plays a role in the urea cycle. It is not incorporated into proteins during translation. Ornithine is abnormally accumulated in the body in ornithine transcarbamylase deficiency, a disorder of th ...

''N''-Acetylglutamate synthase (NAGS) synthesis

''N''-Acetylglutamate synthase is an enzyme that serves as a replenisher of ''N''-acetylglutamic acid to supplement any ''N''-acetylglutamic acid lost by the cell through

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

or degradation. NAGS synthesizes ''N''-acetylglutamic acid by catalyzing the addition of an acetyl group from

acetyl-coenzyme A Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized fo ...

. In prokaryotes with non-cyclic ornithine production, NAGS is the sole method of ''N''-acetylglutamic acid synthesis and is inhibited by arginine. Acetylation of glutamate is thought to prevent glutamate from being used by

proline Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the p ...

biosynthesis.

Vertebrates

In contrast to prokaryotes, NAGS in mammals is enhanced by arginine, along with

protamine Protamines are small, arginine-rich, nuclear proteins that replace histones late in the haploid phase of spermatogenesis and are believed essential for sperm head condensation and DNA stabilization. They may allow for denser packaging of DNA ...

s. It is inhibited by ''N''-acetylglutamic acid and its analogues (other ''N''-acetylated compounds). The brain also contains ''N''-acetylglutamic acid at trace amounts, however no expression of NAGS is found. This suggests that ''N''-acetylglutamic acid is produced by another enzyme in the brain that is yet to be determined.

Biological roles

Vertebrates and mammals

In vertebrae and mammals, ''N''-acetylglutamic acid is the allosteric activator molecule to mitochondrial carbamyl phosphate synthetase I (CPSI) which is the first enzyme in the urea cycle. It triggers the production of the first urea cycle intermediate, carbamyl phosphate. CPSI is inactive when ''N''-acetylglutamic acid is not present. In the liver and small intestines, ''N''-acetylglutamic acid-dependent CPSI produces

citrulline The organic compound citrulline is an α-amino acid. Its name is derived from '' citrullus'', the Latin word for watermelon. Although named and described by gastroenterologists since the late 19th century, it was first isolated from watermelon in ...

, the second intermediate in the urea cycle. Liver cell distribution of ''N''-acetylglutamic acid is highest in the mitochondria at 56% of total ''N''-acetylglutamic acid availability, 24% in the nucleus, and the remaining 20% in the cytosol. Aminoacylase I in liver and kidney cells degrades ''N''-acetylglutamic acid to glutamate and acetate. In contrast, ''N''-acetylglutamic acid is ''not'' the allosteric cofactor to carbamyl phosphate synthetase found in the cytoplasm, which is involved in

pyrimidine Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The oth ...

synthesis. ''N''-acetylglutamic acid concentrations increase when protein consumption increases due to the accumulation of ammonia that must be secreted through the urea cycle, which supports the role of ''N''-acetylglutamic acid as the cofactor for CPSI. Furthermore, ''N''-acetylglutamic acid can be found in many commonly consumed foods such as soy, corn, and coffee, with cocoa powder containing a notably high concentration. Deficiency in ''N''-acetylglutamic acid in humans is an autosomal recessive disorder that results in blockage of urea production which ultimately increases the concentration of ammonia in the blood (

hyperammonemia Hyperammonemia, or high ammonia levels, is a metabolic disturbance characterised by an excess of ammonia in the blood. Severe hyperammonemia is a dangerous condition that may lead to brain injury and death. It may be primary or secondary. Ammoni ...

). Deficiency can be caused by defects in the NAGS coding gene or by deficiencies in the precursors essential for synthesis.

Bacteria

''N''-Acetylglutamic acid is the second intermediate in the arginine production pathway in ''

Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...

'' and is produced via NAGS. In this pathway, ''N''-acetylglutamic acid kinase (NAGK) catalyzes the phosphorylation of the gamma (third) carboxyl group of ''N''-acetylglutamic acid using the phosphate produced by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

adenosine triphosphate Adenosine triphosphate (ATP) is a nucleoside triphosphate that provides energy to drive and support many processes in living cell (biology), cells, such as muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all known ...

(ATP).

White clover seedling roots

''Rhizobium'' can form a symbiotic relationship with white clover seedling roots and form colonies. The extracellular ''N''-acetylglutamic acid produced by these bacteria have three morphological effects on the white clover seedling roots: branching of root hairs, swelling of root tips, and increase in the number of cell divisions in undifferentiated cells found on the outer-most cell layer of the root. This suggests that ''N''-acetylglutamic acid is involved in the stimulation of mitosis. The same effects were observed on the strawberry clover, but not in

legume Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consum ...

s. The effects of ''N''-acetylglutamic acid on the clover species were more potent than the effects from

glutamine Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...

, glutamate, arginine, or

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

Structure

''N''-Acetylglutamic acid is composed of two carboxylic acid groups and an amide group protruding from the second carbon. The structure of ''N''-acetylglutamic acid at physiological pH (7.4) has all carboxyl groups deprotonated.

Proton NMR spectroscopy

The molecular structure of ''N''-acetylglutamic acid was determined using proton NMR spectroscopy. Proton NMR reveals the presence and functional group location of protons based on

chemical shift In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of ...

s recorded on the spectrum.

¹³C NMR spectroscopy

Like proton NMR, carbon-13 (¹³C) NMR spectroscopy is a method used in molecular structure determination. ¹³C NMR reveals the types of carbons present in a molecule based on chemical shifts that correspond to certain functional groups. ''N''-Acetylglutamic acid exhibits carbonyl carbons most distinctly due to the three carbonyl-containing substituents.

References

External links

Diagram at biochemj.org
{{DEFAULTSORT:Acetylglutamic acid, N- Acetamides Dicarboxylic acids Amino acid derivatives