The properties and identification of proteins.

protein is the material basis of life, is one of the most important biological molecules of living organisms, all life activities are inseparable from protein. The study of the structure, properties and function of proteins is the core problem of life science. Understanding proteins starts with understanding the properties of proteins and further mastering techniques for identifying and isolating proteins in samples using the properties of proteins. This experiment mainly introduces the basic method of qualitative identification of whether the sample contains protein and protein precipitation separation.

, coloring reaction of protein

"Experimental Purposes

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"experimental principle"

Any compound containing two or more alamide-based (-CO-NH2) in a molecule, or similar groups, such as -CH2-NH2, -CS-NH2, -C (NH) NH2, may react with more interference factors, whether directly connected by such groups or indirectly by a carbon or nitrogen atom. NH3 has serious interference with this reaction because NH3 and copper ions produce dark blue copper ammonia mates. It should be noted that both proteins andhave a double peptide reaction, but substances with a double peptide reaction are not necessarily proteins or peptides.

equipment and reagents

"Procedure"

(ii) three ketone reaction

< text-align: left; > "Experimental Principles

α-amino acids and proteins tri ketone reaction in two steps, first amino acids are oxidized, producing CO2 and aldehyde, while hydrationtridone is reduced to a also prototypethromonone; the second step is to produce a prototype thromone with another hydrate tritone molecule and ammonia shrink to produce a colored substance. The suitable pH for this reaction is 5 to 7, the same concentration of protein or amino acids in different pH conditions of different color depth is different, acids spent too large or even color. The reaction is very sensitive, 1:1 500 000 concentration of amino acid aqueous solution can show the reaction, so it is a commonly used amino acid quantification method. The

" (operation steps

II, protein precipitation reaction

Under the influence of certain physical and chemical factors, protein molecules lose hydration film or loss of charge, and lose the stabilization factor, that is, in solid form from the solution, this effect is called protein precipitation.

(2) irreversible precipitation effect: in the precipitation reaction, the internal structure of protein molecules, spatial configuration is destroyed, lost its original natural properties, at which point the protein has been denatured. The precipitation of this denatured protein can no longer be dissolved in the original solvent and is called irreversible precipitation reaction. Heavy metal salts, alkaloid reagents, pericic acids, over-alkalis, heating, shock, ultrasound, organic solvents can all cause irreversible precipitation reactions to proteins.

"Experimental Principles

protein is hydrophosphate, under the influence of high concentrations of neutral salt, protein molecules are dehydrated by salt, while the charge of protein molecules is neutralized, resulting in the protein collosian stability is destroyed and precipitated. Neutral salts do not destroy the molecular structure and properties of proteins, so the resulting proteins remain naturally protein-like and can be dissolved again when neutral salts are removed or reduced in concentrations.

"Equipment and Reagents"

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"Experimental Principles
Nitrogen-alkaline compounds with significant physiological effects in plants are called alkaloids (or plant alkalis). Substances that can precipitate alkaloids or produce color reactions with them are called alkaloid reagents, such as tantalum, bitter acid, phosphorus tungsten acid, etc. Protein in the aqueous solution is acid-base electrolytes, protein solution pH is less than the isoelectric point, the alkaline base of protein molecules with more positive charge, it can be combined with the negative charge in alkaloid reagents to form insoluble and precipitation. Alkaloid reagents, as well as triclosan and sulfonyl salivary acid, are important in blood and urine analysis, blood chemistry titration, often used as a reagent to remove proteins, to eliminate protein interference with the determination.

"Equipment and Reagents"
1. 1:10 egg white solution.
2. 10% HCl solution.
3. 10% NaOH solution.
4. 10% sulfonyl sulphate solution.

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(1) take test tube 1, add 1:10 egg white solution 1 ml, 10% HCl1 drop, mix well, and add 10% sulfonyl hydrolytic acid solution 2 drops.
(2) also observed the precipitation of two tubes of protein.
(iii) Heavy metal salt precipitation protein

The pH of the protein solution is greater than the isoelectric point, the acidic base group of the protein molecule has more negative charge, easy to be positively charged heavy metal salt Cu2 plus,