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    Home > Biochemistry News > Biotechnology News > The metabolism of ammonia

    The metabolism of ammonia

    • Last Update: 2020-11-03
    • Source: Internet
    • Author: User
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    the name
    (i) the source of ammonia 1.
    amino acids in
    amino acids
    decomposition in tissue
    are desamined by combined deamination or other ways, which is the main source of ammonia in the tissue.The amino acids in
    tissues produce amines by dehydrogenic reaction, and then free ammonia and corresponding aldehydes by monoamine oxidase or amine oxidase, which is a secondary source of ammonia in the tissue, and the ammonia produced by the breakdown of amino acids in the tissue is the main source of ammonia in the body. This part of
    also increases
    the amount of ammonia produced when there is too much protein in the diet.2. When glutamine flows through the kidneys from the kidney source, it can be broken down by glutamine (glutaminase) in the epithet cells of the renal tube to produce glutamate and NH3.this part of NH3 accounts for about 60% of the kidneys' ammonia production. Various other amino acids also produce ammonia by breaking down in the epithal cells of the renal tube, accounting for about 40% of the kidneys' ammonia production.in the epithal cells of the renal tube have two paths: excreted into the primary urine and excreted with the urine, or re-absorbed into the blood to become blood ammonia. Ammonia is easily passed through the biofilm, while NH4 is not easily passed through the biofilm. Therefore, the path of ammonia production in the kidneys is determined by the relative pH of blood and primary urine. The pH of the blood is constant and therefore actually determines the pH of the original urine.
    the original urine pH partial acid, the NH3 and H-plus discharged into the original urine become NH-4, with the urine excreted from the body. If the pH of the original urine is high, NH3 is easily re-absorbed into the blood. Clinically, patients with increased blood ammonia should be aware of this when using diuretics.3. Intestinal source of ammonia This is the main source of blood ammonia. Under normal circumstances, 15.0% of urea synthesized by the liver is secreted into the intestinal cavity through the mucous membranes of the intestines. Gut bacteria have urea enzymes that hydrolyz urea into CO2 and NH3, part of which accounts for about 90 percent of total intestinal ammonia production (about 4 grams per day for adults).
    can be absorbed into the blood, three-and-a-half of which is in the colon and the rest in the empty intestine and back intestine. Ammonia into the blood can be through the door vein into the liver, re-synthetic urea. This process is called urea's intestinal liver circulation (enterohepatin circulation of urea).small amount of ammonia in the gut comes from the effects of corruption. This refers to the process by which food proteins that are not digested and absorbed or their hydrolytic products, amino acids, break down under the action of gut bacteria. The products of corruption are amines, ammonia, phenols, pyridine, H2S and other harmful substances to human body, but also can produce substances beneficial to human body, such as fatty acids, vitamin K, biotin and so on.The degree of re-absorption of NH3 into the blood in the intestines is determined by the pH of the contents of the intestines, when the pH value of the intestines is less than 6, the ammonia in the intestines produces NH4, which is excreted with feces, and when the pH in the intestines is higher than 6, ammonia in the intestines is absorbed into the blood. Clinically for patients with high blood ammonia enema treatment, taboo use of soapy water, so as not to aggravate the disease.(ii) the way of ammoniaammonia is a toxic substance, the human body must timely convert ammonia into non-toxic or less toxic substances, and then excreted. The main route is to synthesize urea in the liver, excrete with urine, some ammonia can be synthesized glutamine and mendonamide, can also be synthesized with other non-essential amino acids, a small amount of ammonia can be directly excreted through urine. Ammonia in urine is good for acid excretation.(iii) Transport of ammonia 1. Glucose-alanine circulation: Acetone as a metastasis amino subject in muscle tissue, which is produced and transported by blood to the liver. In the liver, acetone acid is produced by transamino action, glucose can be produced by sugar isogenetic action, glucose is transported from the blood to muscle tissue, broken down metabolism to produce acetone acid, the latter then accept amino production of alanine.
    this cycle pathway is called "Alanineglucose Cycle". In this way, the muscle amino acid NH2 base is transported to the dirty to Synthesize urea with NH3 or tyrosine.this cycle, the incompletely decomposed product of ammonia and glucose in muscle tissue, acetone, is transported to the liver in the form of non-toxic alanine as a glycogenic raw material. Glucose produced by the opposite sex in the liver can be used by muscles or other exoded tissues. 2. Ammonia and glutamate are catalyzed by glutamine synthase (glutamine) and transported by blood to the liver or kidneys, which are then hydrolyzed into glutamine and ammonia. Glutamine mainly transports ammonia from the brain, muscles and other tissues to the liver or kidneys. (iv) Urea Synthesis According to animal experiments, it has long been determined that the liver is the main organ of urea synthesis and the kidneys are the main organ of urea excretion. In 1932, Krebs et al. used rat liver
    slices
    for in-body experiments and found that urea could be synthesized from CO2 and ammonia under the condition of energy supply.
    adding a small amount of arginine, birdine, or guarine to the reaction system can speed up the synthesis of urea, which is not reduced. To this end, Krebs et al. proposed the theory of birdine cyclicc. Ratner and Cohen then elaborated on their responses. The birdine cycle can be summarized as: two N-atoms in urea are provided by ammonia and tyrosine respectively, while C atoms are from HCO-3, five-step enzymatic reaction, two-step mitochondrials, three steps in cell fluid. Its detailed process can be divided into the following five steps: 1. Synthesis of aminomethyl phosphate aminomethyl phosphate is in the presence of Mg, ATP and Nacetyl glutamate (AGA), by aminomethylphosphate synthesis enzyme I (carbamylphosphate i, CPSI) catalyticizes the synthesis of NH3 and HCO-3 in the mitochondrials of liver cells. two types of CPS: (1) mitochondrial CPS-I. using free NH3 to synthesize aminomethyl phosphoric acid for nitrogen sources and participate in urea synthesis. (2) Cell fluid CPS-II., using glutamine as an N-source, involved in the synthesis of niacin from the beginning. The CPS-I. catalytic response includes the following three steps. (1) ATP active HCO-3 produces ADP and carbonyl sulfate (carbonyl phosphate) (2) NH2 with carbamate, which replaces sulfates with carbamate and Pi. (3) 2nd ATP
    Phosphate
    to produce aminomethyl phosphoric acid and ADP. this reaction is irreversible and consumes 2 molecules of ATP. CPS1 is a variant enzyme, and AGA is an enzyme variant activator. It is made up of acetylCoA and glutamate. reactions to glutamate
    dhydrogenase
    and aminomethyl phosphate synthase I catalysis in the mitochondrials of liver cells are closely coupled. Glutamate dehydrogenase catalytic glutamate oxidation deamining, the resulting products are NH3 and NADH plus H. NADH is oxidized by the NADH oxidative respiratory chain to produce H2O, and the energy released is used for ADP phosphate to generate ATP.
    therefore glutamate dehydrogenase catalytic reaction not only provides the substrate NH3 for the synthesis of amino methyl phosphoric acid, but also provides the energy ATP required for the reaction. Aminomethyl phosphate synthase I converts toxic ammonia into aminomethyl phosphoric acid, and the ADP generated in the reaction is also a variant activator of glutamate dehydrogenase, which promotes further oxidation of glutamate deaminate.
    this close association is conducive to the rapid fixation of ammonia in the hepatocellular mitochondrial body, preventing ammonia from escaping out of the granules into the plasma, and then through the cell membrane into the blood, causing the blood ammonia to rise. 2. Production of guarine (citrulline): urethane
    transferase
    (ornithine transcarbamoylase) is present in mitochondrials, usually with CPS-I enzyme-forming complex catalytic aminomethyl phosphate transmethylate to produce guarine in birds. (Note: Birdine, guarine are not standard α-amino acids, do not appear in proteins). This reaction is carried out in the mitochondrial body, and birdine is produced in the cytosine, so it is necessary to enter the mitochondrial body through a specific permeable system. 3. Synthesis of argininosuccinate. guarine passes through the mitochondrial membrane into the cytoplasm, in which argininosuccinate synthase (Argininosuccinate Synthetase) catalyzes the argininosuccinate and the amino contraction of tyrosine to produce a second nitrogen atom in the urea molecule. This reaction is supplied by ATP. 4. Arginine's generation argininosuccinase catalytic argininosuccinase catalytic arginine serum acid cleavage into arginine and yanhusoic acid The Yanhuso acid generated in the above reaction can be regenerated by oxalic acid through the intermediate steps of the triacetic acid cycle, and then regenerated by glutamate
    paraenzyme
    catalytic arginine. Thus, by Yanhuso acid and tyrosine, the triacetic acid cycle is associated with the urea cycle. 5. The final reaction of the urea cycle is to produce urea from arginase(arginase) catalytic arginase hydrolysis to produce urea and regenerate birdine, which then enters the mitochondrials to participate in another cycle. urea synthesis is an energy-consuming process, the synthesis of 1 molecule urea requires the consumption of 4 high-energy phosphoric acid bonds. (3 ATP hydrolyzed to generate 2 ADP, 2 Pi, 1 AMP and PPi). At the urea cycle substrate level, energy consumption is greater than recovery. NADH is produced by L-glutamate dehydrogenase catalytic deamining and Yanhuso acid regeneration of oxalic acid in the winter anthionine reaction. Six ATPs can be produced by mitochondrial reoxidation (Figures 7-8). 6. Regulation of urea circulation CPS-I is a mitochondrial in vivo variant enzyme, the variant activator AGA is catalyzed by Nacetyl glutamate synthase, and hydrolyzed by specific hydrolytic enzymes. The rate at which the liver produces urea is associated with AGA concentration.
    When amino acids break down vigorously, the concentration of glutamate is increased by transamination, increasing the synthesis of AGA, thus activating CPS-I, accelerating the synthesis of aminomethyl phosphoric acid and promoting the urea cycle. Arginine is an activator of AGA synthase, so arginine is used clinically to treat high ammoniaemia. (v) high ammoniaemia and ammonia poisoning normal physiological conditions, blood ammonia is at a low level. Urea circulation is the key to maintaining low concentrations of ammonia in the blood. When liver function is seriously impaired, urea circulation is impaired and blood ammonia concentration increases, called high ammoniaemia. The mechanism of ammonia poisoning is not clear.
    It is generally believed that ammonia enters the brain tissue and can be combined with α ketone diacin to form glutamate, glutamate and ammonia further combined to produce glutamine, thereby reducing α ketone diacine and glutamate, resulting in a weakened cycle of triamcirconate, thereby reducing ATP production in brain tissue.
    glutamate itself is a neurotransmitter and a precursor to another neurotransmitter, γ-aminobutyrate (γ-aminobutyrate, GABA), whose reduction also affects the normal physiological function of the brain and can cause coma in severe cases.

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