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Detection of antigens on nitrocellulose paper immunoblots with monoclonal antibodies.

A very sensitive method for the detection of antigen-antibody complexes on nitrocellulose paper immunoblots is described. The protein antigens are separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by their electrophoretic transfer onto a nitrocellulose sheet ("Western blot"). The protein antigens bound to the nitrocellulose paper are exposed to the monoclonal antibody and the antibody-antigen complexes are detected on the paper by an immunoenzymatic reaction. The improved sensitivity of this method is the result of (i) the use of the detergent Tween 20 in blocking the nonspecific binding of the antibodies to the nitrocellulose paper, (ii) the use of a peroxidase-antiperoxidase (PAP) reaction, and (iii) the intensification of the diaminobenzidine reaction product with nickel and cobalt ions in phosphate buffer.

Animals↗

Transfer of small plasmid DNA fragments from polyacrylamide gels onto nitrocellulose paper.

The incorporation into a 7% polyacrylamide gel of a nucleic acid-specific photochemical reagent 4,5',8-trimethylpsoralen at a concentration of 1 mg/dl of acrylamide solution improves both the sensitivity and the efficiency of the transfer of plasmid DNA fragments from the gel onto nitrocellulose filters. This improvement allows detection by blot hybridization of DNA fragments as small as 57 bp long.

Collodion↗

Comparisons using 35S- and 32P-labeled DNA for hybridization on nitrocellulose filters.

DNA was labeled by nick translation with 35S and used as a probe in Southern- or colony-blot DNA hybridization. Comparison with DNA labeled with 32P showed that not only was 35S-labeled DNA suitable as a probe, but in many cases had advantages. The longer half-life of 35S allows for less stringent timing of experiments and eliminates the waste of unused old label. Resolution on autoradiographs was found to improve when using 35S-labeled DNA.

Chemical Phenomena↗

On the electrotransfer of polypeptides from gels to nitrocellulose membranes.

The conditions which affect the elution of polypeptides from polyacrylamide gels by electrophoresis and polypeptide-nitrocellulose interactions have been studied. The rate of elution of polypeptides from a 15% sodium dodecyl sulfate-polyacrylamide gel is dependent on the molecular weight of the individual polypeptides, which is in agreement with the results of W. N. Burnette (Anal. Biochem. 112, 195 (1981)). We also observed that current density affects the rate of elution. Polypeptides smaller than 20,000 daltons pass through pores of 0.45 microns, but not through the pores of 0.1-microns nitrocellulose membranes during electrophoresis. The nonionic detergent NP-40 inhibits the binding of polypeptides to nitrocellulose and removes prebound polypeptides from the membranes. Amido black and Coomassie blue staining and destaining processes do not remove the bound polypeptides from the membranes, but may affect the antigenicity of polypeptides. Polypeptides immobilized on nitrocellulose can be stored at -70 degrees C for future use.

Antigens, Viral↗

Detection of rare mRNA species in a complex RNA population by blot hybridization techniques: a comparative survey.

The detection of very rare mRNA species in a complex RNA preparation by current RNA blotting techniques is not straightforward. To be able to determine the size of mRNA molecules representing 10(-6) to 10(-7) of the total mass of an RNA preparation, a quantitative comparison of the level of detection of denatured mRNA species electrophoretically separated on agarose gels, followed by transfer to either nitrocellulose or diazobenzyloxymethyl (DBM) paper and hybridization to specific cDNA probes was carried out. Different transfer procedures were analyzed. Optimal conditions have been found which allowed the detection of RNA bands containing as little as 5 pg of a specific sequence within a few days of autoradiography following hybridization with highly labeled [32P]cDNA probes. Using this procedure it was shown that the low amounts of alpha-fetoprotein (AFP) mRNA sequences present in adult rat liver are mature AFP mRNA molecules.

Animals↗

Quantitative binding of covalently closed circular DNA to nitrocellulose in NaI.

A procedure for quantitatively binding covalently closed circular DNA to nitrocellulose is detailed. The procedure involves making DNA saturated with respect to Nat at 25 degrees C, denaturing the DNA by heating to 80-100 degrees C, then passing the DNA-NaI solution through a nitrocellulose membrane at 50-60 degrees C. Form I DNA remains denatured throughout the loading procedure and is quantitatively deposited on the membrane as denatured DNA. The mechanism of binding DNA to nitrocellulose in NaI appears to be different from the binding promoted by NaCl.

Collodion↗

Analysis of receptor-ligand interactions using nitrocellulose gel transfer: application to Torpedo acetylcholine receptor and alpha-bungarotoxin.

A nitrocellulose-gel transfer technique has been adapted to study the interaction of a polypeptide ligand with individual receptor subunits. The acetylcholine receptor isolated from Torpedo californica has been separated into its subunits by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred in a renaturing environment to nitrocellulose sheets. The sheets were incubated with 125I-alpha-bungarotoxin and autoradiographed. A single receptor polypeptide, the alpha subunit (40K) bound the labeled toxin. This binding was demonstrated to be both saturable and specific, although the affinity of 125I-alpha-bungarotoxin (KD, 165 nM) and the potency of d-tubocurarine to displace this binding (IC50, 1 mM) were both reduced by several orders of magnitude when compared to the native receptor.

Animals↗

A microanalytical protein assay using laser densitometry.

Protein content of a wide variety of sample types may be determined by adsorption of microliter samples onto nitrocellulose, followed by amido black staining and laser densitometry. The method is quite rapid, sensitive, and selective, and dispenses with precipitation and transfer steps.

Amido Black↗

Electrophoretic transfer of proteins from fixed and stained gels.

A procedure by which sodium dodecyl sulfate gels can be fixed and stained with Coomassie blue and subsequently transferred to nitrocellulose for immunostaining is outlined. The procedure involves the complete removal of the stain followed by equilibration of the gel in sodium dodecyl sulfate running buffer. The efficiency of transfer is comparable to unfixed gels and the protein pattern of the transfer appears to be sharper, presumably due to less diffusion during the transfer process. The procedure does not affect the antigenicity of the proteins that have been examined by subsequent immunostaining. This method is particularly useful for situations in which sample size or concentration are limiting factors resulting in insufficient material for duplicate gels.

Collodion↗

Blotting intact immunoglobulins and other high-molecular-weight proteins after composite agarose-polyacrylamide gel electrophoresis.

A composite agarose-polyacrylamide gel containing urea and sodium dodecyl sulfate reliably resolved unreduced human immunoglobulins according to their molecular weight. Intact immunoglobulins and a number of other macromolecules were readily transferred to nitrocellulose paper by either capillary or electrophoretic blotting, although the latter technique was more effective. Conventional antigen probing as well as immobilized antibody studies can be performed on the nitrocellulose transfers.

Autoradiography↗

125I-wheat germ agglutinin blotting: increased sensitivity with polyvinylpyrrolidone quenching and periodate oxidation/reductive phenylamination.

Two substantial improvements in sensitivity in the identification of 125I-wheat germ agglutinin-binding glycoproteins on nitrocellulose blots of sodium dodecyl sulfate-polyacrylamide gels are reported. The major improvement in sensitivity (about 30-fold) derives from the use of 2% (w/v) polyvinylpyrrolidone (average Mr 40,000) instead of bovine serum albumin or denatured hemoglobin as the quenching agent (or carrier) during incubation with 125I-wheat germ agglutinin in detergent-free, phosphate-buffered saline. Under these conditions, specific labeling with 125I-wheat germ agglutinin is observed for orosomucoid derivatives that display N-acetylglucosamine or sialic acid residues at the nonreducing termini of their oligosaccharides, as well as for a number of glycoprotein components of a rat hepatocyte plasma membrane fraction. An additional improvement in sensitivity (up to 10-fold) results from an increase in the binding of 125I-wheat germ agglutinin to sialic acid-containing glycoproteins after treatment of the blots with 5 mM sodium metaperiodate followed by 5 mM aniline in the presence of 30 mM sodium cyanoborohydride. This treatment appears to cause the sequential oxidation and reductive phenylamination of the side chain of glycoprotein sialic acid residues.

Amination↗

Quantitation of rabbit cytochrome P-450, form 2, in microsomal preparations bound directly to nitrocellulose paper using a modified peroxidase-immunostaining procedure.

Rabbit hepatic microsomal suspensions were bound directly to nitrocellulose sheets using a "Hybridot" apparatus to ensure uniformity. Cytochrome P-450, form 2, was then detected by a modified immunochemical method wherein the nitrocellulose paper was incubated sequentially with antibody to form 2 for 1 h at 25 degrees C, rabbit anti-goat immunoglobulin G (IgG) at a 1:100 dilution for 15 min at 25 degrees C, goat peroxidase-antiperoxidase at a 1:2000 dilution for 15 min at 25 degrees C, and 3,3'-diaminobenzidine at 0.3 mg/ml plus 0.002% hydrogen peroxide for 30 min at 25 degrees C. These conditions, as opposed to those previously published, yielded less background staining. The density of the stain, scanned with a soft laser (Zeineh), increased linearly from 2 to 100 fmol for purified form 2. Cytochrome P-450, form 2, was detected and quantitated in microsomal samples containing 0.1 to 0.5 and 0.02 to 0.05 micrograms protein for preparations from untreated and phenobarbital-treated rabbits, respectively. The results agreed with those obtained by Western blotting and single radial immunodiffusion. This assay is more sensitive than either Western blotting or radial immunodiffusion and has significant advantages such as ease of operation, increased sample numbers, and reduced interference from extraneous proteins.

Animals↗

A rapid, sensitive method for detection of alkaline phosphatase-conjugated anti-antibody on Western blots.

A rapid, sensitive method has been developed to detect antibody-antigen complexes on "Western blots." The methods of H. Towbin, T. Staehlin, and J. Gordon were used to separate and blot the antigens onto nitrocellulose. The remaining sites of attachment were blocked and the nitrocellulose was washed with polyoxyethylenesorbitan monolaurate (Tween 20). The blot was then reacted with the antiserum or hybridoma supernate to be tested. After the antigen-antibody reaction was completed, the blot was washed and treated with anti-antibody which had been conjugated to alkaline phosphatase. The alkaline phosphatase was detected by the reduction of the tetrazolium salt to diformazan by the hydrogen ions released in the formation of indigo by the reaction of the phosphatase on the indoxyl phosphate. The advantages of this method over previously described techniques are (1) use of Tween 20 allows the blot to be stained with Coomassie blue, (2) the substrates of the alkaline phosphatase reaction are stable for long periods of time, (3) the reaction products form an intense blue color which does not fade, (4) the resolution is extremely good with little to no band broadening, (5) the reaction is sensitive to picogram quantities of antigen, and (6) the reaction is quantitative.

Alkaline Phosphatase↗

Visualization of antigenic proteins on Western blots.

A new technique for the detection of antibodies bound to proteins blotted onto nitrocellulose paper was developed. The method is rapid, sensitive, and does not require radioactive probes. Proteins transferred to nitrocellulose paper are first reacted with primary antibody followed by reaction with an alkaline phosphatase conjugated second antibody. The phosphatase activity is then visualized using an agar gel impregnated with the histochemical phosphatase stain 5-bromo-4-chloro-3-indolyl phosphate (BCIP) (J. P. Horwitz, J. Chua, M. Noel, J. T. Donatti, and J. Freisler (1966) J. Med. Chem. 9, 447; Sigma Chemical Co., Technical bulletin No. 710-EP (1978]. Antigen-antibody complexes give rise to sharp, permanent blue stained bands both on the nitrocellulose paper and in the agar overlay gel. This procedure allows detection of bands containing less than 20 ng of protein.

Antibodies, Monoclonal↗

Detection of lipopolysaccharides in polyacrylamide gels by transfer to nitrocellulose followed by immunoautoradiography with antibody and 125I-protein A: "LPS blotting".

Lipopolysaccharides (LPS), which constitute the somatic (O) antigen of gram-negative bacteria, were used to demonstrate the procedure of LPS blotting involving the electrophoretic transfer of electrophoretically resolved LPS from sodium dodecyl sulfate-polyacrylamide gels to nitrocellulose filters. Immobilized LPS could then be immunoautoradiographically visualized in situ by reaction with specific anti-LPS antibody and subsequent binding of radioiodinated Staphylococcus protein A. LPS blotting is expected to provide an efficient and specific means of investigating the LPS (O) antigens of gram-negative bacteria.

Antibodies, Bacterial↗

A general immunochemical method for detecting proteins on blots.

Following horizontal electroelution, or blotting, of proteins from polyacrylamide gels to immobilizing matrices, such as nitrocellulose or Zeta-bind paper, the transferred proteins can be derivatized in situ with pyridoxal 5'-phosphate and sodium borohydride. After a quenching step to eliminate nonspecific binding of antibody to the protein-binding matrix, the blot is incubated with a solution containing a mouse monoclonal antibody specific for the 5'-phosphopyridoxyl group. The transferred proteins can then be located on the blot with second antibody staining procedures employing either a peroxidase-linked goat anti-mouse F(ab')2 antibody or a peroxidase-linked avidin/biotin system. The solid-phase enzyme-linked immunosorbent assay method described in this report is a mild, general, and sensitive immunochemical method for the detection of proteins on protein-binding matrices.

Animals↗