name pyruvic acid. pyruvic acid. Determination of pyruvic acid in urine by colorimetric method
- an organic acid, the first of a series of α-keto acids, that is, it contains keto groups in the α-position with respect to carboxyl. The anion of pyruvic acid is called pyruvate and is one of the key molecules in many metabolic pathways. In particular, pyruvate is formed as the end product of glycolysis, and under aerobic conditions can be further oxidized to acetyl coenzyme A, which enters the Krebs cycle. In conditions of lack of oxygen and pyruvate is converted in fermentation reactions.
Pyruvic acid is also the starting material for gluconeogenesis, the reverse process to glycolysis. It is an intermediate metabolite in the metabolism of many amino acids, and in bacteria it is used as a precursor for the synthesis of some of them.
Physical and chemical properties
Pyruvic acid is a colorless liquid with an odor similar to that of acetic acid, miscible with water in any proportion.
For pyruvic acid, all reactions of the carbonyl and carboxyl groups are characteristic. Due to their mutual influence on each other, the reactivity of both groups is enhanced, and this also leads to a facilitated decarboxylation reaction (cleavage of the carboxyl group in the form of carbon dioxide) in the presence of sulfuric acid or when heated.
Pyruvic acid can exist in the form of two tautomers, enol and keto, which are easily converted into each other without the participation of enzymes. At pH 7, the ketone form predominates.
Biochemistry
Pyruvate formation reactions
A significant part of pyruvate in cells is formed as the end product of glycolysis. In the last (tenth) reaction of this metabolic pathway, the enzyme pyruvate kinase catalyzes the transfer of the phosphate group of phosphoenolpyruvate to ADP (substrate phosphorylation), resulting in the formation of ATP and pyruvate in the enol form, quickly tautomerizing into the ketone form. The reaction takes place in the presence of potassium and magnesium or manganese ions. The process is expressed exergonic, the standard change in free energy ΔG 0 = -61.9 kJ / mol, as a result of which the reaction is irreversible. Approximately half of the released energy is stored in the form of the phosphodiester bond of ATP.
Also, six amino acids are metabolized to pyruvate:
- Alanine - in the transamination reaction with α-ketoglutarate, catalyzed by Alanine aminotransferase in mitochondria;
- Tryptophan - in 4 steps it turns into alanine, then transamination occurs;
- Cysteine - in two steps: at the first, the sulfhydryl group is cleaved off, the second - transamination;
- Serine - in a reaction catalyzed by serine dehydratase;
- Glycine is only one of three possible degradation pathways, only one ends with pyruvate. The conversion occurs through serine in two steps;
- Threonine - the formation of pyruvate is one of two degradation pathways, carried out through conversion to glycine, and then to serine).
These amino acids are glucogenic, that is, those from which glucose can be synthesized in the body of mammals in the process of gluconeogenesis.
Pyruvate Conversion
Under aerial conditions in eukaryotic cells, pyruvate formed in glycolysis and other metabolic reactions is transported to mitochondria (if it is not synthesized immediately in this organelle, as in the case of alanine transamination). Here it is converted in one of two possible ways: either it enters into an oxidative decarboxylation reaction, the product of which is acetyl-coenzyme A, or it is converted to oxaloacetate, which is the starting molecule for gluconeogenesis.
Oxidative decarboxylation of pyruvate is carried out by a pyruvate dehydrogenase multienzyme complex, which includes three different enzymes and five coenzymes. In this reaction, a carboxyl group in the form of CO 2 is cleaved from the pyruvate molecule, the resulting acetic acid residue is transferred to coenzyme A, and one NAD molecule is also restored:
The total standard change in free energy is ΔG 0 = -33.4 kJ / mol. The generated NADH transfers a pair of electrons to the respiratory electron transport chain, which ultimately provides energy for the synthesis of 2.5 ATP molecules. Acetyl-CoA enters the Krebs cycle or is used for other purposes, such as the synthesis of fatty acids.
Most cells, in conditions of sufficient amounts of fatty acids, use them, and not glucose, as an energy source. Due to β-oxidation of fatty acids, the concentration of acetyl-CoA in mitochondria is significantly increased, and this substance acts as a negative modulator of the pyruvate decarboxylase complex. A similar effect is observed when the energy requirements of the cell are low: in this case, the concentration of NADH increases compared to NAD +, which leads to the suppression of the Krebs cycle and the accumulation of acetyl-CoA.
Acetyl coenzyme A simultaneously acts as a positive allosteric modulator for pyruvate carboxylase, which catalyzes the conversion of pyruvate to oxaloacetate with the hydrolysis of one ATP molecule:
Since oxaloacetate cannot be transported through the inner mitochondrial membrane due to the lack of an appropriate carrier, it is reduced to malate, transferred to the cytosol, where it is oxidized again. The enzyme phosphoenolpyruvate carboxykinase acts on oxaloacetate, which converts it to phosphoenolpyruvate, using the phosphate group of GTP for this:
As you can see, this complex sequence of reactions is the reverse of the last reaction of glycolysis, and, accordingly, the first reaction of gluconeogenesis. This workaround is used because the conversion of phosphoenolpyruvate to pyruvate is a very exergonic neodefense reaction.
In eukaryotic cells under anaerobic conditions (for example, in very active skeletal muscles, submerged plant tissues, and solid tumors), as well as in lactic acid bacteria, the process of lactic acid fermentation occurs, in which pyruvate is the final electron acceptor. Taking a pair of electrons and protons from NADH, pyruvic acid is reduced to lactic acid, catalyzes the reaction of lactate dehydrogenase (ΔG 0 = -25.1 kJ / mol).
This reaction is necessary for the regeneration of NAD +, which is necessary for glycolysis to occur. Despite the fact that, in total, no oxidation of glucose occurs during lactic acid fermentation (the C: H ratio for both glucose and lactic acid is 1: 2), the released energy is sufficient for the synthesis of two ATP molecules.
Pyruvate is also the starting material for other types of fermentation, such as alcoholic, butyric, propionic, etc.
In humans, pyruvate can be used to biosynthesize the substitutable amino acid alanine by transamination from glutamate (the reverse reaction of the transamination described above between alanine and α-ketoglutarate). In bacteria, it is involved in the metabolic pathways for the formation of such essential amino acids for humans as valine, leucine, isoleucine and lysine.
Blood pyruvate level
Normally, the level of pyruvate in the blood ranges from 0.08-0.16 mmol / l. By itself, an increase or decrease in this value is not diagnostic. Usually measure the ratio between the concentration of lactate and pyruvate (L:P). An L: P > 20 may indicate a congenital disorder of the electron transport chain, the Krebs cycle, or a lack of pyruvate carboxylase. L:P<10 может быть признаком дефектности пируватдегдрогеназного комплекса. Также проводят измерения Л: П в спинномозговой жидкости, как один из тестов для диагностики нейрологических нарушений.
Reagents and equipment: tartaric acid (crystal), acid sodium sulfate (anhydrous).
In a mortar, a mixture of tartaric acid and acid sodium sulfate is prepared in approximately a ratio of 3:1. The carefully ground mixture is placed in a test tube, which is closed with a stopper with a drain tube, to which a test tube is brought - a receiver. The mixture is carefully heated until melting, and the resulting pyruvic acid is distilled off into a test tube - a receiver.
Carefully! Make sure that during the foaming of the reaction mixture there is no overturning and no clogging of the gas outlet tube. The distillation is completed when 0.5 - 1 ml of liquid is collected in the receiver. It is tested with litmus paper (what?), diluted with a double amount of water and stored for experiment No. 5.
Reaction equation:
Experiment 5. Preparation of pyruvic acid phenylhydrazone.
Reagents and equipment: pyruvic acid - a solution obtained in experiment No. 4, phenylhydrazine acetic acid - a solution.
To a solution of pyruvic acid, add 1 - 1.5 ml of a solution of acetic acid phenylhydrazine. What's happening? Why? What properties of pyruvic acid characterize this reaction?
Reaction equation:
Experience 6. Properties of acetoacetic ester
Reagents and equipment: acetoacetic ether, bromine water (saturated), 2% iron (III) chloride solution, test tubes.
Add 1-2 drops of acetoacetic ester to the test tube and add 2 ml of distilled water. The mixture is vigorously stirred and 1 drop of a 2% iron (III) chloride solution is added. A violet color gradually develops, which indicates the presence of an enol group in the acetoacetic ester solution. Iron(III) chloride forms a colored complex compound with the enol form.
When a few drops of bromine water are added, the solution becomes colorless, since bromine is added at the double bond, and the hydroxyl group loses its enol character:
After some time, the solution turns purple again, since the binding of the enol form disrupts the dynamic equilibrium, and part of the remaining ketone form of the acetoacetic ester passes into the enol form, forming a colored complex with Fe 3+ ions. Upon repeated addition of bromine water, the discoloration of the solution is again observed, followed by the resumption of the violet color. This process can continue until the mobile hydrogen atoms are completely replaced by bromine, i.e. to obtain dibromoacetoacetic ester, not capable of tautomeric transformations. 
Explain in what cases keto-enol tautomerism is possible.
Experience 7. Interaction of benzoic, cinnamic and salicylic acids with bromine water
Reagents and equipment: saturated solutions of benzoic, cinnamic and salicylic acids, bromine water (saturated); pipettes, test tubes.
1-2 ml of saturated solutions of benzoic, cinnamic and salicylic acids are poured into three test tubes. Add a few drops of saturated bromine water to each test tube. In a test tube with benzoic acid, bromine water does not decolorize, cinnamon and salicylic acids decolorize bromine water:
Describe the mechanisms of these reactions. Explain why benzoic acid does not react with bromine under these conditions.
29 October 2016Pyruvic acid (formula C 3 H 4 O 3) - ?-ketopropionic acid. Colorless liquid with an odor of acetic acid; soluble in water, alcohol and ether. It is usually used in the form of salts - pyruvates. Pyruvic acid is found in all tissues and organs and, being a link in the metabolism of carbohydrates, fats and proteins, plays an important role in metabolism. The concentration of pyruvic acid in tissues changes with liver diseases, some forms of nephritis, cancer, beriberi, especially with a lack of vitamin B1. Violation of the metabolism of pyruvic acid leads to acetonuria (see).
See also biological oxidation.
Pyruvic acid (acidum pyroracemicum) - ?-ketopropionic acid. It exists in two tautomeric forms - ketone and enol: CH 3 COCOOH>CH 2>COHCOOH. The keto form (see Keto acids) is more stable. Pyruvic acid is a colorless liquid smelling of acetic acid, d 15 4 \u003d 1.267, t ° pl 13.6 °, t ° kip 165 ° (partially decomposes at 760 mm). Soluble in water, alcohol and ether. Nitric acid oxidizes to oxalic acid, and chromic anhydride to acetic acid. As a ketone, P. to. gives hydrazone, semihydrazone, oximes, and as an acid it forms esters, amides and salts - pyruvates. It is used most often in the form of pyruvates.
P. to. is obtained by distillation of tartaric or tartaric acids using water-removing agents. Its definition is based on reactions with nitroprusside, salicylaldehyde, 2,4-dinitrophenylhydrazine, the products of which are colored.
Pyruvic acid is found in all tissues and organs. In the human blood, 1 mg% is normal, and in the urine 2 mg%. The item to. plays an important role in a metabolism, being a connecting link of an exchange of carbohydrates, fats and proteins. In P.'s organism to. it is formed as a result of anaerobic decomposition of carbohydrates (see. Glycolysis). Later, under the action of pyruvate dehydrogenase, P. to. turns into acetyl-CoA, which is used in the synthesis of fatty acids, acetylcholine, and can also transfer its acyl to oxaloacetic acid for further oxidation to CO 2 and H 2 O (see Biological oxidation) . P. to. also participates in the reactions of transamination and glycogenolysis.
The concentration of P. to. in tissues changes with a variety of diseases: liver diseases, some forms of nephritis, beriberi, cerebrospinal injuries, cancer, etc.
Violation of P.'s metabolism to. leads to acetonuria.
In pharmacology, pyruvic acid is used to prepare zinhofen.
Source - http://www.medical-enc.ru/15/pyruvic-acid.shtml
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Pyruvic acid (C 3 H 4 O 3) - α-ketopropionic acid. It is usually used in the form of salts - pyruvates. It is the end product of glucose metabolism during glycolysis. One molecule of glucose is converted into two molecules of pyruvic acid. Further metabolism of pyruvic acid is possible in two ways - aerobic and anaerobic. Under conditions of sufficient oxygen supply, pyruvic acid is converted into acetyl-coenzyme A, which is the main substrate for a series of reactions. Pyruvate can also be converted into oxaloacetate in an anaplerotic reaction. The oxaloacetate is then oxidized to carbon dioxide and water. If there is not enough oxygen, pyruvic acid undergoes anaerobic cleavage with the formation of lactic acid. During anaerobic respiration in cells, pyruvate obtained during glycolysis is converted to lactate using the enzyme
lactate dehydrogenase and NADP during lactate fermentation, or acetaldehyde and then into ethanol during alcoholic fermentation. Pyruvic acid is the "intersection point" of many metabolic pathways. Pyruvate can be converted back into glucose through gluconeogenesis, or into fatty acids or energy through acetyl-CoA,
into the amino acid alanine, or into ethanol. For example, a working muscle releases significant amounts of alanine into the blood along with lactic acid. Alanine is formed in muscle from pyruvic acid by transamination. From the bloodstream, alanine is taken up by the liver, converted to pyruvate, and pyruvate is used for gluconeogenesis (glucose-alanine cycle, see Figure 9.24).
Pyruvic acid is found in all tissues and organs and, being a link in the metabolism of carbohydrates, fats and proteins, plays an important role in metabolism. The concentration of pyruvic acid in tissues changes with liver diseases, some forms of nephritis, cancer, beriberi, especially with a lack of vitamin B1. Violation of the metabolism of pyruvic acid leads to acetonuria.
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