''N''-Acetylglutamic acid (also referred to as ''N''-acetylglutamate, abbreviated NAG, chemical formula C₇H₁₁NO₅) is biosynthesized from glutamate and acetylornithine by ornithine acetyltransferase, and from glutamic acid and acetyl-CoA by the enzyme ''N''-acetylglutamate synthase. The reverse reaction, hydrolysis of the acetyl group, is catalyzed by a specific

hydrolase Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are este ...

. It is the first intermediate involved in the biosynthesis of arginine 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 Biochemistry, 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 ...

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

Discovery

''N''-Acetylglutamic acid is an extracellular metabolite 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 cells ...

trifolii that was characterized using many structure determination techniques such as

proton nuclear magnetic resonance Proton nuclear magnetic resonance (proton NMR, hydrogen-1 NMR, or 1H NMR) is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the struct ...

(¹H NMR) spectroscopy,

Fourier-transform infrared spectroscopy Fourier-transform infrared spectroscopy (FTIR) is a technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid, or gas. An FTIR spectrometer simultaneously collects high-resolution spectral data over a wide spectra ...

, and

gas chromatography-mass spectrometry Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

. In ''

'', extracellular build-up of ''N''-acetylglutamic acid is due to metabolism involving

nod factor Nod factors (nodulation factors or NF), are signaling molecules produced by soil bacteria known as rhizobia in response to flavonoid exudation from plants under nitrogen limited conditions. Nod factors initiate the establishment of a symbiotic rel ...

genes on a symbiotic plasmid. 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 glutamate 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 amino acid that plays a role in the urea cycle. Ornithine is abnormally accumulated in the body in ornithine transcarbamylase deficiency. The radical is ornithyl. Role in urea cycle L-Ornithine is one of the produ ...

''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 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 for ...

to glutamate. 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 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 in t ...

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 Carbamoyl phosphate is an anion of biochemical significance. In land-dwelling animals, it is an intermediary metabolite in nitrogen disposal through the urea cycle and the synthesis of pyrimidines. Its enzymatic counterpart, carbamoyl phosphate syn ...

. 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 1 ...

, 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 In enzymology, an aminoacylase () is an enzyme that catalyzes the chemical reaction : N-acyl-L-amino acid + H2O carboxylate + L-amino acid : Thus, the two substrates of this enzyme are N-acyl-L-amino acid and H2O, whereas its two p ...

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 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 is a metabolic disturbance characterised by an excess of ammonia in the blood. It is a dangerous condition that may lead to brain injury and death. It may be primary or secondary. Ammonia is a substance that contains nitrogen. It i ...

). 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. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...

'' 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, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms o ...

(ATP).

White clover seedling roots

''Rhizobium'' can form a symbiotic relationship with

white clover ''Trifolium repens'', the white clover, is a herbaceous perennial plant in the bean family Fabaceae (otherwise known as Leguminosae). It is native to Europe, including the British Isles,Clapham, A.R., Tutin, T.G. and Warburg., E.F. 1968. ''Excursio ...

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 legumes. 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 compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

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 Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.ed ...

Proton NMR spectroscopy

The molecular structure of ''N''-acetylglutamic acid was determined using

proton NMR spectroscopy Proton nuclear magnetic resonance (proton NMR, hydrogen-1 NMR, or 1H NMR) is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the struct ...

. 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 o ...

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