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Artifacts associated with gold staining of polypeptides separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and transferred to nitrocellulose are eliminated by alkylation of reduced samples or by deletion of the reducing agent.
Rapid transfer of electrophoretically separated, high molecular weight proteins from fabric-reinforced, soft, low-concentration polyacrylamide gels (3.5%T, 2.6%C) is described. Polyester fabrics proved useful for gel reinforcement during vertical slab gel electrophoresis. The fabric-reinforced gel retains its dimension during transfer, equilibration and drying, facilitating comparison of protein bands in the separation gel and transfer matrix.
The 45Ca filtration method which allows calcium-binding proteins to be detected after their adsorption to nitrocellulose filters was used to test conditions for improved Western blotting of calmodulin. Our results indicate that dodecyl sulphate is not efficiently removed from calmodulin during electroelution in standard transfer buffers. This detergent disrupts binding of calmodulin to nitrocellulose. Electrotransfer in potassium buffer which precipitates dodecyl sulphate leads to a 6-fold increase in calmodulin retention by nitrocellulose. With this and other modifications, the detection limit of the 45Ca overlay method of Maruyama et al. (J. Biochem. 1984, 95, 511-519) for calmodulin is increased to 0.2 microgram per lane.
A sensitive method is described for the detection of tissue peptides and proteins. They are separated by tissue isoelectric focusing using thin large-pore polyacrylamide gels, containing detergent and dimethylformamide, and are fixed with either glutaraldehyde or formaldehyde in gelatin-coated nitrocellulose membranes using press-blotting. The fixed peptide and protein antigens are visualized by immunoperoxidase staining. The spectrum of fixed tissue constituents may also be used to test antiserum reactivity and specificity in immunocytochemical staining procedures. Isoelectric focusing of 2 microL homogenates of the neurointermediate lobe of the pituitary allowed the immunodetection of peptides and proteins of various sizes and the determination of isoelectric points. However, direct application onto gels of small pieces of frozen tissue sections, sliced in a cryostat, appeared to be more efficient. By direct tissue isoelectric focusing of brain tissue, peptides were effectively eluted and separated from sections up to 100 microns thickness. This allowed the detection of small peptides with a detection limit of approximately 10 pg/section.
An improved procedure, "thermoblotting", is described for transferring proteins by diffusion from PhastGel Gradient media to an immobilizing matrix after horizontal sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After electrophoresis the gels were left on the separation bed of PhastSystem, the blotting matrix was applied and a transfer temperature was selected between 5-70 degrees C. An experimental series at fixed diffusion times showed that the transfer yield was significantly increased with temperature. The evaluation was done visually after staining of the blots with colloidal gold. An evaluation study comparing nitrocellulose, nylon, and polyvinylidenedifluoride of different pore sizes is also reported. Finally, the transfer efficiencies for 125I-labelled bovine serum albumin and soybean trypsin inhibitor were estimated using four different blotting procedures: two diffusion blotting techniques and two electrophoretic blotting techniques (tank vs. semi-dry).
The effect of blocking nitrocellulose membranes with the nonionic detergent Tween 20 on the detection, by protein blotting, of IgE-binding to house dust mite Dermatophagoides pteronyssinus allergens has been investigated. Tween blocking led to enhanced immunodetection of allergens despite removal of proteins from the membrane when compared to protein blocking agents which did not displace transferred components. The enhancement varied with the different mite components and, for one in particular, antigen Der p II, an increase of more than 100-fold in IgE antibody binding occurred despite a concurrent loss of more than 90% of Der p II from the membrane. Both the enhancement of binding and loss of components from the membrane were dependent upon the time course of blocking and the concentration of Tween used.
Transparency of nitrocellulose membranes can be realized by simply impregnating the filters with concentrated Triton X-114. Within a few seconds, protein blots become transparent and can be photographed by transillumination or scanned on a densitometer. Removal of the detergent is possible and the recovered filters can further be used for immunodetection purposes. This procedure is particularly wellsuited where extensive investigation of a single separated protein sample is required.
Enzyme-linked immunofiltration assay (ELIFA) for labeling transferred proteins is an interesting and powerful technique for the rapid specific detection (15 min) of proteins immobilized on nitrocellulose or nylon membranes (0.20 and 0.45 micron). ELIFA does not require fastidious handling of the membranes. Saturation, specific labeling and washing procedures are achieved by filtration, controlled by a monitoring unit which regulates the flow rate and ensures excellent specificity, repetition and reproducibility. The recycling by closed circuit or by repetitive inversion of the flow direction offers the advantage of reducing the volumes of expensive reagents while simultaneously increasing the sensitivity of the technique. The detection limit is at least as low as 1-5 ng using directly or indirectly enzymatically labelled probes. ELIFA may be extended to the identification of glycoproteins using specific ligands such as lectins or to the immunocapture of an antigen using specific antibodies immobilized on an activated membrane. ELIFA complements fast separation, by e.g., isoelectric focusing, polyacrylamide gel electrophoresis, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis and accelerated electrotransfer to membranes with rapid detection reducing the total time for separation transfer and detection to less than 2 h.
The efficiency of semi-dry electrophoretic transfer after sodium dodecyl sulfate (SDS)-electrophoresis using PhastGel media was investigated in a model system using three isotope labelled proteins. To give a full picture of the blotting process the amount of protein present in the gel, membranes, and filter papers was determined after different transfer times. The influence of the transfer buffer, commonly used additives such as methanol and SDS, and several different immobilizing matrices was investigated. Soybean trypsin inhibitor, bovine serum albumin, and ferritin were used as model proteins to study the effect of size on transfer efficiency. Basically, all three stages of the blotting process decide the result; the elution of protein from the gel, the immobilization of protein to the membrane, and the loss of material from the membrane during transfer. A theoretical explanation for the observed poor binding to a second membrane is discussed. Our results show that the buffer composition has little influence on the efficiency of transfer from the gel, but can be significant to the binding capacity of the membrane. In all experiments performed, there was never one moment during the transfer when all protein was eluted from the gel and simultaneously still bound to the membrane. The highest recovery in the membrane was obtained at different time intervals for different proteins. This indicates that quantitative transfer procedures cannot be generalized. However, obtaining an optimal method for reliable quantification of a specific protein or group of proteins is possible. For general protein staining of nitrocellulose and polyvinylidene difluoride membranes, a highly sensitive silver staining method requiring only 15 min has been used.
Bromoperoxidases were investigated by protein blotting after polyacrylamide gel electrophoresis. While the denatured proteins bound to nitrocellulose, the native enzymes did not. Instead, they could be transferred successfully to DEAE-cellulose. Procedures for immunostaining and glycoprotein detection with concanavalin A on DEAE-cellulose are described. The results indicate that binding of native proteins to nitrocellulose can not necessarily be assumed. DEAE-cellulose is suitable both to investigate this phenomenon or as a substitute for nitrocellulose in blotting of native proteins.
Protein purification and characterisation have been age-old problems for the biochemist. A new era has arisen with the advent of one- and two-dimensional gel electrophoresis and high sensitivity automated protein microsequencing. These two tools along with electroblotting have made it possible to separate and analyse complex protein mixtures. We studied six different membranes compatible with Edman degradation chemistry to determine their efficiencies at binding proteins electroblotted from one-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Their overall blotting-sequencing properties were also evaluated. We found that the polyvinylidene difluoride-based membranes out-performed the glass-based and polypropylene-based membranes under our selected experimental conditions. The problems associated with electroblotting and microsequencing are discussed.
A rapid and simple assay for quantification of proteins in sodium dodecyl sulfate-sample buffer is described. Proteins are bound to a nitrocellulose membrane, stained with colloidal silver, and quantified by transmission densitometry. The staining requires 1 microL of protein sample and takes less than 20 min. Good linearity between the staining intensity and amount of proteins is in the range of 5-100 ng.
We increased selectivity in the detection of glycoproteins on nitrocellulose membranes by introducing a washing step using sodium hydroxide solution. Glycoproteins on the nitrocellulose membrane were first oxidized by sodium periodate; biotin hydrazide was then coupled to the aldehyde groups generated in the sugar moiety of the glycoproteins. The membrane was washed twice using sodium hydroxide solution, and avidin-horseradish peroxidase was then coupled to the remaining biotin. This system allows the detection of nanograms of glycoproteins on nitrocellulose membranes, and its specificity allows the clear distinction of glycoproteins from the nonglycosylated protein of bovine serum albumin.
The preparation of homogeneous ultrathin native polyacrylamide gels, using a basic as well as an acidic buffer system is described. The basic buffer system consists of Tris-HC1/Tris-glycine, the same buffer as in sodium dodecyl sulfate (SDS)-gel electrophoresis but without SDS. The acidic system uses potassium acetate, pH 4.3, as gel buffer and beta-alanine, pH 4.6, acetic acid as electrolytes. The gels are covalently bound on glass plates. Binding of acidic gels requires a special pretreatment of glass plates. The whole procedure is simple and extraordinarily fast: 100-120 min from the start of gel preparation to the end of electrophoresis. Coomassie staining is done in 40 min and silver staining in 90 min. The native gels are excellently suited for diffusion blotting. Further attractive properties of these gels are easy handling, simple drying and dimensional stability.
A method is described for electroblotting of proteins, separated by gradient polyacrylamide gel electrophoresis, onto an agarose gel matrix containing specific antibodies. Three proteins of different molecular weight, including human albumin, isolated and in plasma, human plasma transferrin and C3 complement were tested. Immunoblotting on agarose, compared with nitrocellulose, was quantitative and highly sensitive, with small amounts of protein (i.e., 100 pg) being detected. Moreover, albumin aggregates (i.e., dimer, trimer and tetramer) were blotted quantitatively in addition to the monomer, and their percentages were calculated. This method is sensitive, quantitative, reproducible, and includes fewer manipulations; furthermore, it is less expensive and does not require the use of toxic or carcinogenic agents.
A simple method for the transfer of 32P-labeled proteins from dried polyacrylamide gels to small disks of nitrocellulose, nylon or polyvinylidene difluoride (PVDF) is described. Gel pieces containing the desired phosphoprotein are rehydrated in buffer containing sodium dodecyl sulfate (SDS) and sealed in agarose in a glass tube over a supporting gel of polyacrylamide. Protein is transferred upwards through a discontinuous density gradient of SDS-buffer and methanol to a disk of membrane sealed to the mouth of the tube with dialysis membrane. The method allows the concentration of a phosphoprotein present in several gel pieces to a single disk of immobilized membrane. Recovery of phosphoprotein was at least as good as obtained with conventional electroblotting. Application of the method to the analysis of the phosphoamino acid content of the astrocyte marker, glial fibrillary acidic protein, is described.
A high efficiency transfer of the low density lipoprotein (LDL) receptor proteins from polyacrylamide slab gel onto immobilizing nitrocellulose membranes using the horizontal semi-dry electrophoretic system is described. The transfer of the LDL receptors from solubilized rat liver microsomes was performed between two graphite plate electrodes in a continuous buffer system containing methanol and sodium dodecyl sulfate. The protein transfer was achieved in only 150 min at a constant current of 0.8 mA/cm2 at room temperature with very low Joule heat development. The homogeneous electric field yield between the two electrode plates produced a satisfactory transfer of the LDL-receptor protein band in spite of its high molecular weight, and only few protein traces remained in the polyacrylamide gel after blotting. This improved method allows a rapid and quantitative transfer of the LDL receptors without protein denaturation, since the specific binding activity of the blotted receptor is retained as demonstrated by ligand-blotting and immunoblotting.
Nitrocellulose membrane was preactivated with divinyl sulfone, and a spacer of 1,6-diaminohexane was coupled to the membrane which was functionalized by glutaraldehyde, leaving a reactive carbonyl group. The peptides were coupled to the carbonyl by the side chain and terminal amino groups. The octapeptide angiotensin II (sequence: DRVYIHPF) and peptide analogs containing 6-10 amino acid residues were dotted directly onto the matrix at 45 degrees C for 15 min and detected by specific antisera, which were raised in rabbits against angiotensin I and II, respectively. They were visualized by peroxidase-coupled anti-rabbit IgG antibodies. The detection limit for synthetic angiotensin II was 500 fg per cm2 (= 500 amol per cm2) and for the decapeptide angiotensin I (sequence: DRVYIHPFHL) it was 500 pg per cm2 (= 400 fmol per cm2). Separation of synthetic angiotensin analogs by high performance thin-layer chromatography on silica coated aluminum plates was followed by electroblotting onto activated nitrocellulose and detection with specific antibodies, showing a sensitivity of 100 fg and 1 pg for angiotensin II and angiotensin I, respectively. Isoelectric focusing in agarose using Ampholine carrier ampholytes and immunoblotting with specific antisera displayed a lower sensitivity for angiotensin II and angiotensin I of 2 ng and 20 ng, respectively. The isoelectric focusing and immunoblotting technique was applied for separation of angiotensin I and II and related peptides in serum, where synthetic angiotensin I was degraded in the presence of 1 mM phenylmethylsulfonyl fluoride and 10 mM ethylenediaminetetraacetic acid.(ABSTRACT TRUNCATED AT 250 WORDS)