The method of determining the structure of protein level one.

< p class "tt1" > is an important breakthrough < the development of > ofmolecular biology in the region. At present, the first-level structure of nucleic acid research, because Sanger and other inventions of addition and subtractation, can be developed by leaps and leaps. In this regard, the first-level structure of protein research progress is not as rapid as nucleic acids.

but with the Edman liquid phase automatic sequence analyzer and solid phase sequence analyzer and gas phasechromatography < "> mass spectrometrography (GCMS) and other methods appear. The speed of structural analysis is also significantly accelerated. So far, the first-level structural analysis of nearly a thousand proteins has been completed. Not only is the sample usage reduced, but the staff is also significantly reduced.

That year Sanger analyzed insulin spent a full ten years, today the use of automated instruments, analysis of a molecular weight of about 100,000 proteins only need a few days, it can be seen that the application and development of new technologies to promote scientific development, protein-level structural determination methods and monograph literature more, here only briefly summarized.

protein molecules of the first-level structure determination, summarized to include peptide chain separation, degradation, peptide segment separation and sequential analysis and -S-S-positioning.

first-level structure determination method can be summarized as follows:

1. the separation of the polypeptide chain

before determining the structure of a protein, first of all, must ensure the purity of the protein under test, so that the results are accurate and reliable. Secondly, we should understand its molecular weight and sub-base, according to its sub-base to divide the protein into several peptide chains.

1) peptide chain unpacting

protein molecular polypeptide chain connection has co-price binding and non-co-price binding two kinds. In order to break apart the polypeptide chain of -S-S-connected at a co-price, the chemical treatment methods that must be used are:

(1) permeric acid oxidation

break-S-S-with oxidant permeic acid. This reaction is usually carried out for about 2 hours at 0 degrees C, and both Ss can be converted into sulfonates, so that the oxidized cysteine is called sulfonyl alanine.

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if cysteine is present in protein molecules at the same time, it can also be oxidized into sulfonyl alanine. In addition, methionine and tryptophan can also be oxidized, increasing the complexity of analysis.

(2)-based ethanol reduction

using reducing agent -based ethanol can also make the protein -S-S-break. When high concentrations of -based ethanol can be reduced to H after a few hours of room temperature in pH8? At the same time, the reaction system also needs to have 8 molars or 6 molars of hydrochloric acid to denature the protein, peptide chain loose into an irregular configuration, at which point the reducing agent can act on -S-S-. This reaction is reversible, so for the reaction to be complete, the concentration of dredging ethanol must be 0.1-0.5 moles.

(3) Clelandreagents reduction effect

Cleland' s points to dmission Dithioerythriotol and dithiothriotol are strong reagents in redox ability, as long as 0.01 moles can make the protein-S-S-reduction, the reaction is basically similar to dredging ethanol, and in many globulin reactions, can not be denatured agents.

Cleland reagent first forms intermediates with the protein -S-S-, the reaction is eventually, the reducing agent is oxidized to form a stable hep ring compound, the protein is reduced.

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reduced protein instability, SH-based regeneration-S-S-key is extremely easy to oxidize. The methods for stabilizing SH-based

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(A) alkylation reagents transform SH-based into stable sulfur ether derivatives.

If iodine-based acetylamide replaces iodine-based acetic acid, the product of which S-acetamine methyl derivatives are not charged, sulfonate can also react with histamine, methionine and lysine, but the reaction conditions are different, can be controlled by a variety of pH and reaction time.

(B) ammonia ethylization

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protein molecules of several peptide chains if non-co-priced health combination, then with urea, hydrochloric acid and other denatured agents can be disassembled. After the polypeptide chain of protein is removed, it is separated and purified, generally using gelfiltering, ion exchange, electrophoresis and other methods, I would like to repeat.

< the end of each peptide chain > the separation and purification of the p class." < the end analysis methods of >p class" "biao3" >2) are more, here we only introduce the more commonly used several.

(1) N-end assay

A. nitrofluorobenzene (FDNB, DNFB): Sanger proposed this method in 1945, which is one of his important contributions.

DNP-amino acids are drawn with organic solvents, it can be identified by the layering position what kind of amino acids it is. Sanger used this method to determine that the N ends of insulin were glycine and phenylalanine, respectively.

B. Cyanate method: In 1963 Stank and Smyth introduced a new method for determining the end of N, the steps are as follows:

The endolyceride amino acid is not charged, so it can be separated from the free amino acid by ion exchange layering method, the isolated acetylamide amino acid is hydrolysed by hydrochloric acid, regenerate the free amino acid, identify this amino acid can understand what kind of amino acid N-end.

C. dimethylamide sulfonyl chloride: In 1956 Hartley and others reported a sensitive method for determining the N-end, using 1-dimethylamide-5-sulfonyl chlorine, or dansulphate. It acts on the end of free amino, similar to Sanger's DNFB method, and is derived from sulfonamide.

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has a strong yellow fluorescence. The advantages of this method are high sensitivity (100 times higher than FDNB method, sample size is less than 1 nanogram molecule) and higher stability of dan sulfonamide (higher hydrolysis stability of acids than DNP amino acids), can be used paper electrophoresis or polyamide film lithography identification.

(2) C-end analysis

A. solution: This is the most commonly used method for determining C-ends. The peptide is dissolved in aqueous radon and reacts at 100 degrees C, resulting in the release of the amino acids at the end of the carbie as free amino acids, while the rest of the peptide chain part is associated with the production of amino acids.

so that the amino acids at the end of the carboxy can be divided and analyzed by method of withdrawal or ion exchange layering. If the side chain of the amino acids at the end of the caramigne is with amides such as winteramide and glutamine, the free end amino acids at the end of the caramignide cannot be produced during the solution. In addition, care should be taken to avoid any small amount of hydrolysing, so as not to confuse the release of amino acids with end analysis.

< p class s"tt1" >B. pyridinease hydrolyzing method: pyridinease can be specifically hydrolyzed nixyl end amino acids. Depending on the specificity of the enzymatic solution, it can be distinguished into pyrethroidases A, B and C. When applying pyrethroidase to determine the end, the dynamic experiment of the enzyme needs to be carried out in advance in order to select the appropriate enzyme concentration and reaction time, so that the released amino acids are mainly C end amino acids.

3) amino acid composition analysis

< "tt1" > before further analysis of the amino acid sequence of the peptide chain, first of all, should understand which amino acids it is composed of, how many amino acids each? The methods of analysis are:

(1) layering method

the peptide chain is completely acidic hydrolyzed into free amino acids, and then Dansyl markers, polyamide thin-film layering, this method is a super-micro-analysis in protein structure analysis, but this method is not accurate enough for quantitative analysis.

(2) ion exchange layering method

Spaekman and so on developed a precise amino acid parts of the quantitative method. They use sulfonate-type ion exchange resin, which is a high molecular weight of solid polystyrene, with a large number of functional groups, sulfonate base in low pH and low ion strength conditions, according to the acid base of amino acids, amino acids with positive electricity, so replace the resin na^-, with the help of electrostatic action and binding to sulfonate base.

because of the various amino acids on the resin affinity is different, so when changing the solution pH and ion strength, they can be washed out in turn and separated, and quantitative determination. On this basis, an amino acid automatic analyzer was developed. With the development of science and technology, amino acid automatic analyzer in the sample dosing, separation speed and detection capacity has also been greatly improved. At present, the best instrument sample analysis volume as long as dozens of Picomole, analysis time as long as dozens of minutes, and the calculation of all automation, to study the protein first-level structure has brought great convenience. the amino acid composition of the

"biao2" >2. the degradation of the peptide chain

the amino acid composition of the peptide chain is often more complex, so it is difficult to directly analyze the amino acid sequence of peptides, using the polypeptide chain to further degrade into smaller fragments, and then analyze. The cracking of peptide bonds is an important problem in the research work of primary structure, which requires less lysate points, strong selectivity and high reaction yield.

1) chemical method

< "tt1" > (1) brominated cyanide method is the ideal chemical method, can selectively break methionine is located in the peptide bond

< classp"tt1" >brominated hydrogen chemical degradation method its advantages: < p . > (1) the general protein contains less methionine, so you can obtain a large fragment

(2) single-specific strong

"tt1" > (3) yield of more than 80%

(4) mild conditions, in room temperature for a few hours to ten.

(2) partial hydrolytic acid

Sanger used this method in the analysis of insulin's first-stage structure, i.e. 0.1N hydrochloric acid at 110 degrees C or 6 N hydrochloric acid at 37 degrees C hydrolysing. This partial acid hydrolyzing method is not very specific and therefore not suitable for large fragments of proteins and peptides.

(3) hydroxyamine method

< "tt1" > this method has been attracting attention for nearly a decade, hydroxyamine can specifically crack AsnGly's peptide bonds, acidic conditions crack Asn-Pro peptide bonds. has been used for the analysis of certain proteins.

(4) N-Bromide method

"tt1" > the main cleavage of the peptide bonds at try, more research in the fifties. However, because it can also break the TyrHis peptide bond, it is not widely used.

< p class s"biao3" >2) enzymatic solution

ase hydrolysing method has more advantages than chemical method, so.