Amino acid oxidases catalyze the removal of amino groups by using molecular oxygen, facilitating the oxidation of the carbon skeleton.
Aspartate is formed when an amino group is transferred to oxaloacetate from an amino acid, typically involving alpha-ketoglutarate as the alpha-keto acid.
Transamination is the process of transferring amino groups to α-ketoglutarate, facilitating the conversion of amino acids.
In the fasting state, glucagon inhibits the export of NAG from mitochondria to the cytosol, preventing its degradation.
Oxidative deamination of glutamate is a process where the amino group is removed from glutamate, producing free ammonium and α-ketoglutarate.
A biochemical process where an amino group is transferred from an amino acid to an alpha-keto acid, forming a new amino acid and a new alpha-keto acid.
An enzyme that catalyzes the reaction where aspartate condenses with citrulline to form argininosuccinate, consuming ATP in the process.
Glutamate can cause hyperexcitation in the central nervous system if it crosses the blood-brain barrier, making it potentially harmful.
L-amino acid oxidases in snake venom oxidize amino acids, generating hydrogen peroxide, which supports blood clotting.
Oxaloacetate produced in the citric acid cycle can be transaminated to regenerate aspartate, facilitating the cycling of the carbon skeleton.
The typical concentration of amino acids in blood is around 50 micromol/l.
Aldimine is a type of Schiff base formed between an aldehyde group and an amino group.
Acylation of proteins involves the attachment of acetyl or succinyl groups to lysine side chains, modifying their activity, which can lead to inhibition or activation of the proteins.
An indirect deamination process of any of the 12 amino acids through transaminase reactions.
During glycine degradation, one of its carbon atoms is transferred to folic acid, which is important for the transfer of single carbon units.
Hydrogen peroxide generation is problematic in normal amino acid metabolism, but can be utilized in specific functions, such as in snake venom to support blood clotting.
Transdeamination is a process that releases free ammonia from amino acids, contributing to nitrogen metabolism.
CPS1 is the key target for regulation by sirtuins.
A Schiff base is a compound formed by the reaction of an aldehyde group with an amino group, resulting in an aldimine.
Covalent modification, such as phosphorylation or acylation, alters enzyme activity by either activating or inhibiting the enzyme, depending on the specific modification.
N-acetyl-glutamate (NAG) is an allosteric activator formed from glutamate that regulates the activity of carbamoyl phosphate synthetase (CPS1) and determines the rate of urea synthesis.
In tissues, glutamate can be converted to glutamine, which is inert and does not affect the central nervous system.
NAD concentration affects the deacylation of CPS, and its degradation in the sirtuin reaction necessitates its regeneration.
Adenylate deaminase removes ammonia from the amino group of adenine, allowing the cycle to close and restore IMP.
The ornithine cycle is a series of biochemical reactions in the liver that synthesizes urea from ammonia and bicarbonate, facilitating the removal of excess nitrogen from amino acid breakdown.
Transamination is the process where an amino group from one amino acid is transferred to a keto acid, typically involving α-ketoglutarate, resulting in the formation of glutamate.
Glycine can be formed from serine in unlimited quantities, allowing for the release of nitrogen in the form of free ammonia through the glycine cleavage system.
Ketimine is formed when the double bond in a Schiff base is translocated, resulting in a compound between a keto group and pyridoxal amine.
α-Ketoglutarate acts as a common acceptor of amino groups during transamination reactions.
Inosinic acid (IMP) is a nucleotide formed when ribose-5 phosphate is attached, serving as an entry point in nucleotide synthesis.
The purine nucleotide cycle releases ammonia indirectly through the breakdown of adenylosuccinate and the recycling of aspartate.
Direct deamination of serine allows for its synthesis in unlimited quantities, starting from a glycolytic intermediate.
The exchange of citrulline and ornithine occurs in the mitochondrial membrane, allowing citrulline to exit the mitochondria for further reactions in the cytosol.
α-Ketoglutarate generated from the oxidative deamination of glutamate can be utilized as a carbon skeleton in gluconeogenesis.
It serves as an alternative source of free ammonia, which is necessary for glutamine synthesis in muscle tissue.
Sirtuins catalyze the removal of acyl groups from lysine side chains, converting inactive acetylated enzymes into their active forms, using NAD in the process.
The reaction consumes ATP, generating AMP, which is thermodynamically equivalent to the breakdown of two high-energy bonds due to the hydrolysis of pyrophosphate (PPi).
ASL is an enzyme that breaks down argininosuccinate into arginine and fumarate.
Glutamine, proline, and glutamate can be converted to citrulline in the intestine, which is then utilized in the urea cycle.
The synthesis of urea occurs only in the liver.
A process called transdeamination that involves two steps: transamination and transdeamination, which helps in removing nitrogen in a nontoxic form.
CPS1 (Carbamoyl Phosphate Synthetase 1) is the rate-limiting enzyme in the urea cycle that regulates the synthesis of urea and adjusts the activity of the cycle to the requirement of nitrogen release.
Arginine activates the enzyme NAGS, which generates NAG, an allosteric activator of CPS1, thereby increasing the activity of the ornithine cycle and urea synthesis.
The liver converts released nitrogen into urea, which is then excreted from the body.
In the fasting state, there is more Nampt activity, resulting in increased NAD formation, which activates sirtuins to deacylate CPS.
Acidosis influences the breakdown of glutamine in the kidney.
Ornithine transcarbamylase (OTC) catalyzes the reaction that converts carbamoyl phosphate into citrulline, which is a key step in the urea synthesis process.
Ammonia is formed as a simplest way to remove nitrogen, but it is toxic and must be kept at extremely low concentrations in the blood to prevent harmful effects, especially in the brain.
Glutamate dehydrogenase is an enzyme that catalyzes the oxidative deamination of glutamate, resulting in the formation of free ammonium and α-ketoglutarate.
An enzyme that catalyzes the direct release of free ammonia from serine, generating pyruvate.
Glutamine serves as an excellent non-toxic form of nitrogen, facilitating the transfer of amino groups and preventing the accumulation of nitrogen in circulation.
Glutamine transfers ammonia to the kidney and liver, playing a crucial role in nitrogen metabolism.
Nampt is the enzyme that regenerates NAD from nicotinamide and is controlled by glucagon.
α-ketoglutarate acts as a keto acid that accepts the amino group from amino acids during the first step of their degradation.
D-amino acid oxidases are enzymes that eliminate D-amino acids, which are toxic and can block enzymes specialized for L-amino acids.
Free ammonium is not problematic in the kidney as it can be directly released in urine, making it an effective solution for nitrogen removal.
The synthesis of one urea molecule consumes a total of 4 ATP molecules, with 2 ATP used in the formation of carbamoyl phosphate and additional ATP consumed in subsequent steps.
A process where amino groups are removed directly from amino acids, such as glycine and histidine, resulting in the release of ammonia.
Glutamine synthetase catalyzes the reaction that synthesizes glutamine from free ammonium (NH4+) and ATP, helping to prevent nitrogen accumulation in circulation.
The rate of deacylation by sirtuins is determined by the level of NAD, which is not saturated in the reaction.
Urea is synthesized through the ornithine cycle, where one nitrogen comes from free ammonia and the second nitrogen comes from aspartate.
OTC is also regulated by the levels of NAD, similar to CPS.
D-amino acids are toxic because they block enzymes that are specialized for L-amino acids by binding to their active sites, preventing proper metabolism.
During fasting, there is excessive breakdown of amino acids, and the ornithine cycle is crucial for converting the carbon skeletons from amino acids into urea for excretion.
Glucagon induces the enzyme Nampt, leading to increased NAD formation during the fasting state.
Carbamoyl phosphate is formed by the incorporation of free ammonia and bicarbonate, and it is the first step in the urea synthesis process, occurring in the mitochondrial matrix of the liver.
Acetylation of CPS renders the enzyme inactive, and its activity can be restored by the removal of the acetyl group by sirtuins.
Fumarate is released during the breakdown of argininosuccinate and can enter the citric acid cycle.
90% of nitrogen is excreted from the body in the form of urea, which is synthesized in the liver.
The synthesis of urea is activated when there is excessive breakdown of amino acids, ensuring the cycle is active under these conditions.
Aspartate collects amino groups from different amino acids and donates them to hypoxanthine, facilitating ammonia release.
The continuous process in all tissues where proteins are degraded and amino acids are either recycled or used for the synthesis of small molecules.
In the kidney, glutamine undergoes hydrolysis by the enzyme glutaminase, releasing free ammonia, which can be excreted in urine.
Glutamine carries nitrogen from extrahepatic tissues, primarily skeletal muscles, to the kidney or liver, where it can be processed further.
Fumarate is released as a carbon skeleton during the breakdown of adenylosuccinate, which can then enter the TCA cycle.
Glutamine is synthesized from free ammonia released during the purine nucleotide cycle, which is crucial for maintaining its synthesis.
Adenylosuccinate synthetase catalyzes the condensation of aspartate with hypoxanthine using GTP, leading to the formation of adenylosuccinate.
The enzyme that catalyzes the formation of carbamoyl phosphate is carbamoyl phosphate synthetase, which uses free ammonia as a substrate.
Pyridoxal phosphate is a coenzyme that is required for the transamination reaction, as it is attached through a Schiff base to a lysine side chain in the active site of the enzyme.
