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    Home > Biochemistry News > Biotechnology News > Metabolism of sulfur-containing amino acids.

    Metabolism of sulfur-containing amino acids.

    • Last Update: 2020-10-29
    • Source: Internet
    • Author: User
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    The namecontains sulfur
    amino acids
    there are three kinds of methionine, cysteine and cysteine, methionine can be converted to cysteine and cysteine, the latter two can also be mutually variable, but the latter can not become methionine, so methionine is essential amino acids.(i) Methionine metabolism 1. Transmethylation and methionine cycle Methionine contains S methyl, can participate in a variety of transmethyl reactions to produce a variety of methyl-containing physiologically active substances. In
    adenosine transferase
    catalyzed with ATP to produce S-adenosine methionine (S-adenosgl methiomine, SAM). Methyl in SAM is highly activated, called active methyl, sam is called active methionine.. SAM can be catalyzed by different methyl
    transferase
    (methyl transferase) to a variety of methyl recipients to form a number of methyl
    compounds
    , such as epinephrine, choline, beetline, carnitine, creatine, etc. are obtained from SAM methyl. SAM is the most important methyl supply in the body.. SAM transfers out of methyl to form S adenosyl homocystine, SAH water explains that adenosine becomes homocysteine (homocystine, hCys). Homocysteine accepts methyl regeneration methionine provided by N5 H3 F4, forming a circular process called methionine cycle. The physiological significance of this cycle is that methyl in methionine molecules can be provided indirectly through N5 H3 H4 by other non-essential amino acids to prevent the high consumption of methionine (Figures 7-15).7-15 S-Adenosine Methionine Cycle N5-CH3FH4 Coenzyme of the same type of cysteine methyl transferase is methyl B12. Vitamin B12 deficiency can cause methionine circulation to be blocked. Clinically, it can be seen that vitamin B12 deficiency causes macrocytocytotic anemia. Noronha and Silverman first proposed the methyl trap thesis in 1962, and Herbert and Zaulsky later revised it. This the theyology holds that: due to vitamin B12 deficiency, resulting in methyl B12 deficiency, so that methyl transfer enzyme activity is low, methyl transfer reaction blocked lead to folic acid in the form of N5-CH3FH4 accumulation in the body. In this way, other forms of folic acid consumption, with these folic acid as coenzyme enzyme activity decreased, affecting the synthesis of alkaloids and thymus, and thus affect the synthesis of
    nucleic acids
    , causing cytocytocyte anemia. In other words, the effects of vitamin B12 on nucleic acid synthesis are indirectly achieved by affecting folic acid metabolism.Although methionine cycle can produce methionine, but the body can not synthesize the same type of cysteine, can only be transformed by methionine, so the body can not actually synthesize methionine, must be supplied by food.homocysteine can also be reduced to cystathione (cystathionine) catalysis with serine to produce cystathione, and then hydrolysis by cysthyl etherase to produce cysteine, α-ketone butyric acid and ammonia. α-ketone butyric acid is converted to monocrystyl CoA, which produces glucose through the triacetic acid cycle, so methionine is a raw sugar amino acid.. 2. Synthetic creatine and creatine phosphate play an important role in energy storage and utilization. The mutual change of the two makes the ATP supply in vivo have the reserve potential. Crea acid is synthesized in the liver and kidneys and is widely distributed in skeletal muscles, heart muscles,
    and
    tissues. Creaine is based on glycine as the skeleton, arginine provides -based, SAM-supply methyl, in -based transferase and methyl transferase catalytic synthesis. At creatine
    kinase
    (creatine phosphohinase, CPK) catalysis, ATP is transferred to creatine molecules to form creatine phosphate (CP) reserves (Figures 7-16).7-16 metabolism of creatic acid CPK consists of two sub-base; There are three isoenzymes, mm type (in skeletal muscle) BB type in the brain) and MB type (in the heart muscle). When myocardial infarction, the activity of MB-type CPK in the blood increases, which can be used as one of the indicators of auxiliary diagnosis.of creatine and creatine metabolism is creatinine, or creatinine for short. Normal adults, the daily amount of creatinine in the urine is constant. When kidney dysfunction, check the creatinine content in the blood or urine to help diagnose it.(ii) Metabolism of cysteine and cysteine 1. Intervulation of cysteine and cysteine Cysteine contains -SH), cysteine contains disulfur bonds (S-S-), both of which can be mutually variable by redoxing. Cysteine is not involved
    synthesis
    protein, which is dehydrogenated from cysteine residue oxidation. The desulfur bonds formed between two cysteine residues in protein molecules play an important role in maintaining protein molecular composition. The cysteine base in protein moleculesthe active group of many proteins or enzymes.2. Cysteine decomposition metabolism of cysteine in the human body is mainly reduced to acetone acid in two ways. One is the direct oxidation route catalyzed by hydrogen peroxygenase, or cysteine sulfonate, and the other is the 3--based acetone acid route through transamination.. 3. Active sulfate metabolism Sulfur amino acids after decomposition metabolism can produce H2S, H2S oxidation into sulfuric acid. Cysteine andcan also be oxidized to produce sulfonyl, and then to produce sulfuric acid. Some of them are excreted from the urine in the form of inorganic salts, and some are activated to produce 3' adenosine phosphate-5'-phosphorenate sulphuric acid (3'-phosphoadenosine 5'-phosphosulfate, PAPS), or active sulfate. . The nature of PAPS is lively and plays an important role in the bio-transformation of the liver. For example, the steroid
    progrogen
    can be inactivated by binding to PAPS into sulfates, and some exogenous phenols can also form sulfates to increase their solubility to benefit from urination. In addition, PAPS can also be involved in the synthesis of sulfate polysaccharides in molecules such as ketones sulfate and cartilage sulfate. . 4. The synthetic glutathione (glutathiose, r glutamyl Cysteinglglycine, GSH) is a tripeptide containing γ-alamide bonds, consisting of glutamate, cysteine and glycine. The synthesis of GSH γ through the γ-glutamyl cycle, proposed by Meister, also known as the Meister cycle (Figures 7-17). γ-glutamine cycle has a dual effect, one is the recomposition of GSH, and the other is through the synthesis and decomposition of GSH exonymic amino acids actively transferred to cells. 7-17 γ-Glutamine Cycle GSH synthesis is catalyzed by γ-glutamine cystein synthase (γ-glutamylcystein synthetase) and GSH synthase (GSH synthetase). Supplied by ATP hydrolysing. In the decomposition of GSH γ-glutamine transpeptidease (γ-glutamyl transpeptidease), γ-glutamyl cyclotransfase (γ-gltamyl cyclotransforase) and 5oxyproprolinase and an intracellular peptidease (protease). . GSH plays an important role in human detoxification, amino acid transport and metabolism. GSH's active group is -based on its cysteine residue, GSH has oxidation and also prototype two forms, can be mutually variable. reaction to glutathione reductase, coenzyme is NADPH, the ratio of GSH to GSSG in cells is 100:1. GSH protects the ability of certain proteins enzyme molecules from oxidation, thus maintaining their biological activity. If red blood cells contain more GSH, it plays an important role in protecting the integrity of red blood cell membrane and promoting the reduction of high iron hemoglobin to hemoglobin. In addition, peroxides and freelances produced in the body can also be removed by selenium-containing GSH peroxidase, e.g.



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