毛细管无胶筛分电泳

围绕着毛细管无胶筛分电泳的介质和机理,概括介绍了近年来这种技术在各个方面的发展,及其在DNA片段的分离、PCR扩增产物的检测和蛋白质分子量的测定等方面的应用前景．     

On-line combination of capillary isoelectric focusing and capillary non-gel sieving electrophoresis using a hollow-fiber membrane interface: a novel two-dimensional separation system for proteins

A novel two-dimensional (2D) separation system for proteins was reported. In the system, a piece of dialysis hollow-fiber membrane was employed as the interface for on-line combination of capillary isoelectric focusing (CIEF) and capillary non-gel sieving electrophoresis (CNGSE). The system is similar equivalent to two-dimensional polyacrylamide gel electrophoresis (2D PAGE), by transferring the principal of 2D PAGE separation to the capillary format. Proteins were focused and separated in first dimension CIEF based on their differences in isoelectric points (pIs). Focused protein zones was transferred to the dialysis hollow-fiber interface, where proteins hydrophobically complexed with sodium dodecyl sulfate (SDS). The negatively charged proteins were electromigrated and further resolved by their differences in size in the second dimension CNGSE, in which dextran solution, a replaceable sieving matrix instead of cross-linked polyacrylamide gel was employed for size-dependent separation of proteins. The combination of the two techniques was attributed to high efficiency of the dialysis membrane interface. The feasibility and the orthogonality of the combined CIEF-CNGSE separation technique, an important factor for maximizing peak capacity or resolution elements, were demonstrated by examining each technique independently for the separation of hemoglobin and protein mixtures excreting from lung cancer cells of rat. The 2D separation strategy was found to greatly increase the resolving power and overall peak capacity over those obtained for either dimension alone.     

Separation and detection of closely related peptides by micellar electrokinetic chromatography coupled with electrospray ionization mass spectrometry using the partial filling technique

Closely related peptides such as neurotensin and angiotensin analogues were separated by capillary zone electrophoresis using a nonionic surfactant, sucrose monododecanoate, as a micelle forming reagent. These peptides were detected by an on-line coupled mass spectrometer using an electrospray ionization interface. However, the presence of the micelles in the separation solution drastically reduced the sensitivity of the mass spectrometer. Therefore, a partial filling technique was employed to prevent the micelles from entering the mass spectrometric interface. A part of the capillary from the injection end was filled with the micellar solution in this technique. Analytes passed through the micellar zone during the electrophoresis and when the separated analytes reached the detection end of the capillary, the micellar zone was still behind the analyte zones, because the nonionic surfactant moved very slowly in acidic conditions. Thus the technique was very useful for mass spectrometric detection for CE when the micellar solution was employed for separation. The optimization of separation and detection conditions was investigated.     

Gas-phase sequencing after electroblotting on polyvinylidene difluoride membranes assigns correct molecular weights to myoglobin molecular weight markers

Commercially available polypeptide marker kits containing peptides generated by cyanogen bromide cleavage of either horse heart myoglobin or sperm whale myoglobin have been investigated by sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE), followed by electroblotting on polyvinylidene difluoride membranes, and gas-phase sequencing. It could be shown that the molecular weights assigned to the SDS-PAGE bands by the companies are incorrect. Arranged in descending order, the marker kits are composed of the following polypeptide fragments from myoglobin: positions 1-153, 1-131, 56-153, 56-131, 1-55, and 132-153. A polypeptide comprising residues 1-14 was not found. According to these results the log Mr versus Rf plot used for calibration must be revised. For the separation of low molecular weight polypeptides and peptides a new gel system based on the theory of multiphasic zone electrophoresis combined with a modified Coomassie staining procedure is reported.     

Improvement of an in-gel tryptic digestion method for matrix-assisted laser desorption/ionization-time of flight mass spectrometry peptide mapping by use of volatile solubilizing agents

The combination of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), in-gel enzymatic digestion of proteins separated by two-dimensional gel electrophoresis and searches of molecular weight in peptide-mass databases is a powerful and well established method for protein identification in proteomics analysis. For successful protein identification by MALDI-TOF mass spectrometry of peptide mixtures, critical parameters include highly specific enzymatic cleavage, high mass accuracy and sufficient numbers and sequence coverage of the peptides which can be analyzed. For in-gel digestion with trypsin, the method employed should be compatible both with enzymatic cleavage and subsequent MALDI-TOF MS analysis. We report here an improved method for preparation of peptides for MALDI-TOF MS mass fingerprinting by using volatile solubilizing agents during the in-gel digestion procedure. Our study clearly demonstrates that modification of the in-gel digestion protocols by addition of dimethyl formamide (DMF) or a mixture of DMF/N,N-dimethyl acetamide at various concentrations can significantly increase the recovery of peptides. These higher yields of peptides resulted in more effective protein identification.     

The structural subunit of glucose-6-phosphate dehydrogenase (baker's yeast).

The subunit molecular weight of glucose-6-phosphate dehydrogenase (G6PD) from baker's yeast has been evaluated. The subunit molecular weight value is shown to be 25,500 daltons by analytical ultracentrifugation, SDS-polyacrylamide gel electrophoresis, and the number of peptides produced by CNBr cleavage. The number of NADP binding sites was determined to be one per 25,500 dalton unit.     

Capillary electrophoretic separation of proteins and peptides by ion-pairing with heptanesulfonic acid

Heptanesulfonic acid as ion-pairing agent was used for the separation of mixtures of low and high molecular mass peptides/proteins by capillary electrophoresis. The separation conditions used were: capillary 37 cm (30 cm to the detector) x 75 microm i.d., voltage 10 kV, phosphate buffer 50 mmol/l, ion-pairing agent heptanesulfonic acid at three different concentrations, namely, 0, 20 or 100 mmol/l, pH 2.5. The separation reflected the ion-pairing equilibria between the ion-pairing agent and the peptide/protein analytes. The influence of ion-pairing on sample mobility (running time) was more pronounced in case of the higher-molecular peptides as compared to the low molecular ones. This difference offers the possibility to separate low and high molecular peptides/proteins that under the absence of the ion-pairing agent would co-migrate. The principle of this approach was demonstrated on a randomly selected set of peptides/proteins; the practical applicability was demonstrated on a set of CNBr peptides arising from a naturally occurring mixture of collagen types I and III.     

Denaturing Urea Polyacrylamide Gel Electrophoresis (Urea PAGE)

Urea PAGE or denaturing urea polyacrylamide gel electrophoresis employs 6-8 M urea, which denatures secondary DNA or RNA structures and is used for their separation in a polyacrylamide gel matrix based on the molecular weight. Fragments between 2 to 500 bases, with length differences as small as a single nucleotide, can be separated using this method¹. The migration of the sample is dependent on the chosen acrylamide concentration. A higher percentage of polyacrylamide resolves lower molecular weight fragments. The combination of urea and temperatures of 45-55 °C during the gel run allows for the separation of unstructured DNA or RNA molecules.In general this method is required to analyze or purify single stranded DNA or RNA fragments, such as synthesized or labeled oligonucleotides or products from enzymatic cleavage reactions.In this video article we show how to prepare and run the denaturing urea polyacrylamide gels. Technical tips are included, in addition to the original protocol ^1,2.     

Capillary isoelectric focusing coupled with dynamic imaging detection: A one-dimensional separation for two-dimensional protein characterization

Here, we devised a novel approach for two-dimensional (2D) protein characterization using a single one-dimensional separation followed by a second characterization in the same instrument. The approach combines capillary isoelectric focusing (CIEF), which separates proteins according to pI, with dynamic imaging detection, which permits monitoring of protein diffusion in real time and thereby allows estimation of molecular weight from diffusion coefficient. Compared with classical 2D gel electrophoresis, the approach provided several significant advantages including speed and ease in operation and automation, while yielding comparable accuracy. The approach was applicable for protein samples of low to moderate complexity.     

Peptide mapping by capillary electrophoresis with Pluronic F127

Separation of peptides and proteins by capillary zone electrophoresis suffers from the interaction of these solutes with the capillary wall which results in the formation of broad peaks and low resolution. To minimize the protein/peptide-capillary wall interaction we tried to use Pluronic F127, a triblock copolymer of the general formula (polyethylene oxide)(x)(polypropylene oxide)(y)(polyethylene oxide)(z) when x=106, y=70 and z=106 which can be considered a surfactant capable of self-association both into isotropic and anisotropic gels. The analytes studied were enzymatic digests (obtained by trypsin or pepsin treatment) of insoluble matrix proteins from avian eggshell. The best separations were obtained by a system exploiting 10% Pluronic F127 in 20 mmol/l phosphate buffer, pH 2.5. Electrophoretic peptide profiles obtained were very complex owing to the complicated nature of the samples (the exact composition of the proteinous insoluble part of the eggshell is still unknown). The separation in phosphate buffer only offered complex maps of incompletely resolved peaks. The use of Pluronic F127 distinctly improved the separation with a considerably better resolution regarding both the number of peaks obtained and the quality of the separation.     

Kinetics of enzyme-catalyzed oligopeptide cleavage monitored by capillary zone electrophoresis: Comparison to spectrophotometric and HPLC methods

Summary A capillary zone electrophoresis method has been developed for monitoring the rate of cleavage of basic oligopeptides. This method is particularly applicable to monitoring the cleavage rate of peptides where the specificity of the proteinase dictates against the presence of bulky chromophores. The kinetic parameters determined for the cleavage of a related chromophoric substrate were directly comparable. The kinetic analysis of intrinsically or mutationally induced inefficient enzymes can be facilitated by this approach.     

The cyanogen bromide peptides of the apoprotein of low density lipoprotein (ApoB): its molecular weight from a chemical view.

After >95% cleavage of the apoprotein (apoB) of the low density lipoproteins with cyanogen bromide, the peptides produced are shown to be extensively aggregated in sodium dodecyl sulfate. Both high temperature and increased concentration (5%) of the detergent are necessary to shift the aggregated peptides from high molecular weight (>25,000) to lower molecular weight aggregates as seen on sodium dodecyl sulfate polyacrylamide gel electrophoresis. End group analyses of the cyanogen bromide digestion by automated sequencer techniques indicate the presence of five (5) methionines. With a known methionine content of 16 moles/100,000 g protein, the molecular weight of the apoprotein must be approximately 30,000.     

Studies on the characterization of the sodium-potassium transport adenosine triphosphatase. Purification and properties of the enzyme from the electric organ of Electrophorus electricus

An unspecific carboxylesterase was purified 180-fold from acid-precipitated human liver microsomes. The final preparation was homogeneous on disc electrophoresis and polyacrylamide gel electrophoresis in the presence of 6.25 M urea at pH 3.2. A single symmetrical peak was also found on gel filtration and on velocity sedimentation in the analytical ultracentrifuge, whereas slight heterogeneity was observed on isoelectric focusing.The amino acid composition of the purified enzyme is presented. From the results the partial specific volume (0.745 ml × g^?1) and the minimal molecular weight (60,000) could be calculated. Fingerprint maps of tryptic peptides from the carboxymethylated enzyme are shown.The molecular weight as determined by gel filtration, disc electrophoresis, and analytical ultracentrifugation is in the range of 181,000–186,000. For the molecular weight of the subunits a value of 61,500 has been obtained by sodium dodecylsulfate polyacrylamide gel electrophoresis. The equivalent weight of the enzyme has been estimated to be 62,500 from stoichiometry of its reaction with diethyl-p-nitrophenyl-phosphate. Partial cross-linking of the subunits with dimethyl suberimidate and subsequent sodium dodecylsulfate polyacrylamide gel electrophoresis yielded three bands with molecular weights of 60,000, 120,000, and 180,000.From these results it is concluded that human liver esterase is a trimeric protein. It is composed of three subunits of equal size, and there is one active site per subunit.     

The complete amino acid sequence of the beta-subunit of protocatechuate 3,4-dioxygenase from Pseudomonas aeruginosa.

The complete amono aicd sequence of the beta-subunit of protocatechuate 3,4-dioxygenase is presented. The beta-subunit contained 237 amino acid residues, 4 of which were methionines. Accordingly, cyanogen bromide cleavage of the S-carboxymethylated beta-subunit produced five peptides. The sequences of these peptides were determined by analyses of the peptides obtained by tryptic, staphyloccal protease and thermolysin digestions. The alignment of the cyanogen bromide peptides was deduced by the use of overlapping peptides containing methionine which were obtained by tryptic digestion of the S-carboxymethylated beta-subunit. The calculated molecular weight was 26,588, which is close to the value estimated by acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate.     

Capillary electrochromatographic separation of aromatic amino acids possessing peptides using porphyrin derivatives as the inner wall modifiers

Two different porphyrin derivatives (H2TPP(m-OPh)4 and Rh(III)TPP(m-OPh)4) were investigated with respect to their capability to help resolution of five model aromatic peptides in capillary electrophoresis/open tubular capillary electrochromatography. Though the main separation mechanism was preferentially based on the ionic properties of the separated analytes, involvement of particularly H2TTPP(m-OPh)4-peptide interactions at alkaline pH (8.0) was clearly demonstrated. In combination with Tris-phosphate buffer, a speed up of the separation was observed at pH 2.25 (particularly if Rh(III)TPP(m-OPh)4 was used as capillary coating); in spite of the speed up of the separation the selectivity of the system was sufficient and resulted in a complete separation of the five model peptides. It can be expected that Rh(III)TPP(m-OPh)4 capillary coating in combination with Tris-phosphate buffer can be generally used for a considerable speeding up of lengthy separations of peptides in acidic media with some decrease in the separation power of the system.     

Structural studies on yeast 3-phosphoglycerate kinase. Isolation by affinity chromatography and characterization of the peptides produced by cyanogen bromide cleavage. Location of the single cysteinyl residue in the primary structure.

Cyanogen bromide cleavage of yeast 3-phosphoglycerate kinase yielded four fragments which account for the amino acid composition of the entire molecule. These results are consistent with a single polypeptide chain of molecular weight 42 000. Affinity chromatography on Sepharose-mercurial followed by gel filtration on Sephadex was used with success for separation of peptides. The carboxyl and N-terminal fragments were characterized. The N-terminal fragment contained the single cysteinyl residue of the protein. After cyanylation and subsequent cleavage, this cysteinyl residue was located near position 100.     

An improved method for separation of low-molecular-weight polypeptides by electrophoresis in sodium dodecyl sulfate-polyacrylamide gel

An improved system for SDS-polyacrylamide gel electrophoresis, capable of analyzing polypeptides having molecular weights from 1500 to 100,000 (especially showing high resolving power in the 1500 to 25,000 molecular weight range) is described. The 10 to 18% linear gradient gel containing 7 M urea with an acrylamide:bisacrylamide ratio of 20:1 and the Laemmli discontinuous buffer was used. The use of the gel with a high crosslinkage ratio is shown to be effective in lowering the leakage of low-molecular-weight polypeptides from the gel. This method has facilitated rapid detection of small amounts of low-molecular-weight polypeptides in body fluids by the use of silver stain. A procedure is presented for the elimination of false bands on the gel frequently encountered during silver staining. The separation patterns of enzymatic cleavage products of proteins, uremic plasma, and urines from nephropathy patients are illustrated. This system is also applicable in the separation of lipopolysaccharides and also for the detection of phospholipids.     

Localization of the alpha-chain cross-link acceptor sites of human fibrin

The potential cross-link acceptor sites of fibrin were specifically labeled with the fluorescent, substitute cross-link donor monodansyl cadaverine (MDC). Several fluorescent alpha-chain peptides generated from enzymatic and cyanogen bromide (CNBr) cleavage of the labeled fibrin were identified by sodium dodecyl sulfate disc gel electrophoresis; they were isolated and then characterized by amino acid analysis, NH2-terminal sequence analysis, and chromatographic and electrophoretic analyses of their digestion products. Ancrod cleavage of MDC-labeled fibrin produced a series of six alpha-chain peptides of molecular weights 34,000 to 12,000, each of which contained an MDC-labeled acceptor site, and an NH2-terminal alpha-chain derivative of molecular weight 37,500. The latter remains disulfide bound in the residual fibrin and has two MDC-labeled sit-s which are separable by CNBr cleavage. Mild plasmin digestion of MDC-labeled fibrin generated fluorescent alpha-chain peptides of molecular weights 45,000, 42,000, 35,000, 23,000, 21,000, and 2,500 in the supernatant and a nonfluorescent NH2-terminal alpha-chain derivative of molecular weight 25,000 which remained in the insoluble residual fibrin. The alignment of these plasmic supernatant peptides was determined from NH2-terminal sequence analyses which indicated that an MDC acceptor site was located at approximately residue 255 of the Aalpha-chain. Cleavage of the MDC-labeled alpha-chain by CNBr, however, localized most of its fluorescence (approximately 80%) to a fragment of molecular weight 29,000 which had the same NH2-terminal sequence as the labeled plasmic peptide of molecular weight 21,000. Both peptides were cleaved by ancrod into two acceptor site-containing peptides of approximately equal fluorescence. The preliminary NH2-terminal sequence analyses of these peptides, when combined with the above findings, indicated that these two other cross-link acceptor sites are in a peptide segment which comprises the middle 17% of the Aalpha-chain.     

Multiplex genotyping and allele frequency estimation in pooled DNAs using non-gel capillary electrophoresis

We present a novel approach of single-nucleotide polymorphism (SNP) analysis in which allele-specific oligonucleotide hybridization is followed by non-gel capillary electrophoresis (ASOH-NGCE) in conjunction with laser-induced fluorescence (LIF). This allows rapid multiplex allelotyping and allele frequency estimation. This method, based on site separation of the hybridization duplexes, retains the simplicity and specificity of ASOH and the homogeneous feature of NGCE with poly(N,N-dimethylacrylamide) (PDMA) as a sieving medium. ASOH-NGCE can be applied to multiplex SNP loci genotyping with excellent separation of hybridization mixtures. Average relative standard deviations (RSDs) were low for within-day (1.10%) and between-day (2.41%) reproducibility. Moreover, the allele frequencies in pooled DNAs were accurately determined from peak areas and equilibrium dissociation constants. Our method was highly sensitive in detecting alleles with frequency as low as 1% and in distinguishing allele frequencies differing by 1% between pools. The average value of differences between real and estimated frequencies (accuracy) was only 0.004.     

Fractionation of spectrin by differential precipitation with calcium

The calcium-stimulated ATPase activity of spectrin can be substantially separated from the magnesium-stimulated activity by partial precipitation of spectrin with calcium. The precipitated Ca-ATPase fraction can be dissolved by dialysis against EDTA, and the resulting solution can be polymerized into characteristic spectrin fibrils. The supernatant contains Mg-ATPase and, either before or after dialysis, contains predominantly “torus” forms. The two fractions are essentially identical on gel electrophoresis, being composed primarily of the high molecular weight peptides with a constant level of minor bands. These results imply that the Ca-ATPase is associated firmly with the high molecular weight peptides.