Key takeaways

• Match the lysis buffer to the target: RIPA for most whole-cell work, milder non-ionic detergents where protein interactions must survive, and urea-based buffers for stubborn membrane proteins.
• Add protease and phosphatase inhibitors. Phosphatase inhibitors are non-negotiable for any phospho-specific blot, and are the step most often omitted.
• Quantify protein before adding reducing agent — BCA is incompatible with DTT and beta-mercaptoethanol, and Bradford is incompatible with detergents.
• Normalise by protein mass, not by volume. Equal volumes of unequal lysates is the commonest cause of apparent expression differences that are really loading differences.
• Do not boil multi-pass membrane proteins. At 95 °C they aggregate and disappear from the gel; 37 °C for 30 minutes or 70 °C for 10 gives far better recovery.
• Aliquot before freezing. Repeated freeze-thaw degrades proteins and is a frequent hidden cause of irreproducibility.
• Run a loading control, and be aware that housekeeping proteins are not invariant across all treatments and tissues.

Contents

• Why sample preparation decides the result
• Sample collection and storage
• Choosing a lysis buffer
• Protease and phosphatase inhibitors
• Protein quantification
• Sample buffer and reducing agents
• Denaturation — and when not to boil
• Loading the gel
• Workflow summary
• Troubleshooting
• References
• Choosing reagents
• Frequently asked questions

Reagents for sample preparation

The panel below follows the workflow in order — lyse, prepare, size-reference, normalise, detect.

RIPA

GenieLyse RIPA Lysis Buffer

Lysis bufferCells & tissue

Standard harsh lysis for whole-cell extracts, solubilising cytoplasmic, membrane and nuclear proteins.

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Lysis buffer

Cell Lysis Buffer (ELISA & Western Blot)

Lysis bufferCells & tissue

A gentler alternative validated for both Western blot and ELISA, useful when one lysate serves both.

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Sample buffer

5X SDS Loading Buffer

Sample bufferAll samples

Concentrated Laemmli-type buffer supplying SDS, glycerol and tracking dye at working dilution.

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Ladder

TriColor Prestained Protein Ladder (10–180 kDa)

LadderAll gels

Prestained reference for molecular weight assignment and for monitoring transfer visually.

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β-actin

beta-Actin Rabbit Monoclonal Antibody

Rabbit mAbWB

Loading control for confirming that equal protein was loaded and transferred across lanes.

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WB kit

Lysis-to-Result Western Blotting Detection Kit

Complete kitCells & tissue

Covers lysis through detection in one system, which reduces variability between reagent lots.

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Why sample preparation decides the result

Western blotting separates proteins by size on a gel, transfers them to a membrane, and detects a target with antibodies. Every stage is downstream of sample preparation, and problems introduced there cannot be corrected later. A protein degraded during lysis will not reappear after a better transfer; a dephosphorylated epitope cannot be recovered by a better antibody.

The practical consequence is that most of the decisions worth thinking about happen in the first hour — which buffer, which inhibitors, how the sample is quantified, and how it is denatured. The rest of the protocol is comparatively forgiving.

Sample collection and storage

Proteolysis begins the moment cells are disrupted, so speed and temperature control matter more than technique elegance.

• Cultured cells. Wash in cold PBS to remove serum proteins, then lyse directly on ice. Scraping into cold buffer is preferable to trypsinising, which itself is a protease treatment and can cleave surface targets.
• Tissue. Homogenise in cold lysis buffer with inhibitors present from the outset. Keep the sample frozen or on ice throughout; thawed tissue degrades quickly.
• Blood, serum and plasma. Process immediately or freeze at −80 °C. Note that serum and plasma are dominated by albumin and immunoglobulin, so low-abundance targets may need depletion or enrichment.
• Storage. Snap-freeze and hold at −80 °C. Aliquot first — each freeze-thaw cycle costs signal, and repeatedly thawing one tube is a common and invisible source of drift across an experiment.

Choosing a lysis buffer

Buffer choice is the first real decision, and it is governed by where the target protein sits and whether its interactions need to survive.

If the target is unfamiliar, RIPA is the sensible default. If it is a receptor or transporter, expect to need a chaotropic buffer and a gentler denaturation step. And if downstream immunoprecipitation of an intact complex is planned, RIPA will destroy what you are trying to capture.

Protease and phosphatase inhibitors

The original advice to include protease inhibitors is correct but incomplete, and the omission is consequential.

Protease inhibitors prevent the target being cleaved by enzymes released on lysis. A broad-spectrum cocktail covers serine, cysteine and metalloproteases; add it fresh to cold buffer, since several components have short half-lives in aqueous solution.

Phosphatase inhibitors are equally important and far more often forgotten. Cellular phosphatases remain active in lysate and will strip phosphate groups within minutes. If the blot is for a phospho-specific target — phospho-ERK, phospho-p38, any activation-state readout — omitting them will produce a blank or weak band that is easily misread as absence of signalling. Include sodium orthovanadate or a comparable tyrosine phosphatase inhibitor together with sodium fluoride or beta-glycerophosphate for serine and threonine phosphatases.

Keep everything on ice throughout. Inhibitors slow degradation; they do not stop it, and temperature does most of the work.

Protein quantification

Quantification exists to let you load equal protein per lane. Without it, comparisons between lanes are uninterpretable.

The two incompatibilities matter in opposite directions and catch people out constantly. Quantify before adding reducing agent. RIPA lysate can be measured by BCA but not reliably by Bradford; once DTT or beta-mercaptoethanol has been added, BCA is no longer valid. The practical order is therefore: lyse, clear by centrifugation, quantify, then add sample buffer with reducing agent — not the reverse.

Always build a standard curve with the same buffer as the samples, since buffer components shift absorbance and a curve made in water will systematically misreport lysate concentration.

Sample buffer and reducing agents

Laemmli-type sample buffer supplies four things, each with a purpose:

• SDS denatures proteins and coats them in negative charge roughly proportional to length, so electrophoretic mobility reflects size rather than native charge or shape.
• Glycerol increases density so the sample sinks into the well instead of dispersing into the running buffer.
• Tris-HCl buffers the sample at the pH the stacking gel requires.
• Bromophenol blue tracks the migration front visually.

Reducing agents — DTT or beta-mercaptoethanol — break disulfide bonds so multi-subunit and internally bonded proteins run as single denatured chains. DTT is less odorous and more stable; beta-mercaptoethanol is cheaper and traditional. Either works.

Reduce selectively, though. Some antibodies recognise epitopes that depend on disulfide bonds and will not detect the reduced protein, so non-reducing conditions are occasionally required — check the antibody datasheet before assuming reduction is always correct.

Denaturation — and when not to boil

The standard instruction is to heat samples in reducing sample buffer at 95 to 100 °C for five minutes. For most soluble cytoplasmic and nuclear proteins that is correct and reliable.

It is the wrong instruction for multi-pass membrane proteins. Receptors, transporters, channels and other proteins with several transmembrane domains have long hydrophobic stretches that, at high temperature in SDS, drive irreversible aggregation. The aggregates fail to enter the gel or smear at the top of the lane, and the result reads as absent protein. This is one of the commonest reasons a membrane target refuses to blot despite good antibody and good lysate.

For those targets, heat gently or not at all: 37 °C for 30 minutes, or 70 °C for 10 minutes, generally recovers far more protein. Urea-containing buffers should not be heated above roughly 37 °C at all, because urea decomposes and carbamylates proteins, shifting apparent mass and destroying some epitopes.

After heating, spin briefly to collect condensate and pellet any insoluble material, and load the cleared supernatant.

Loading the gel

• Load equal protein, not equal volume. This is the point of quantification. Twenty to thirty micrograms of total protein per lane suits most targets on a mini-gel; abundant proteins need less, low-abundance targets more.
• Keep total volume within well capacity. Overfilling causes spill into adjacent lanes and cross-contamination that mimics real signal.
• Do not overload. Excess protein distorts band shape, causes smiling and can saturate detection so that genuine differences compress and disappear.
• Include a prestained ladder in at least one lane for size assignment, and to confirm visually that transfer occurred.
• Balance the buffer. Load an equal volume of sample buffer into any empty wells so the gel runs evenly across its width.
• Plan the loading control. Beta-actin, GAPDH or tubulin confirm equal loading and transfer — but they are not universally invariant, and a treatment that alters the cytoskeleton or metabolism can change them. Where that is a risk, a total-protein stain is the safer normaliser.

Workflow summary

The one amendment to make to that sequence: quantification must sit between clearing the lysate and adding sample buffer, because the reducing agent in sample buffer invalidates the BCA assay.

Troubleshooting

• No band at all. Confirm the protein is expressed in that sample type, then check the lysis buffer can solubilise it. For membrane targets, suspect heat aggregation before suspecting the antibody.
• Multiple bands or a smear below the target. Degradation. Use fresh inhibitors, keep everything on ice, and work faster — particularly with tissue.
• Phospho-signal absent while total protein is fine. Almost always missing phosphatase inhibitors, or a lysate left at room temperature.
• Bands at the top of the lane that will not resolve. Aggregation from over-heating, or overloading. Reduce temperature and protein amount.
• Uneven intensity across lanes with an even loading control. Check transfer uniformity and membrane contact rather than the samples.
• Loading control varies with treatment. The housekeeping protein is responding to the treatment. Switch normaliser or use total-protein staining.
• Results drift across an experiment. Suspect freeze-thaw of a shared aliquot, or a standard curve built in the wrong buffer.

References

The methodological foundations of the technique, plus our full protocol and troubleshooting resource:

• Laemmli UK. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature, 1970;227(5259):680–685.
• Burnette WN. “Western blotting”: electrophoretic transfer of proteins from sodium dodecyl sulfate-polyacrylamide gels to unmodified nitrocellulose and radiographic detection with antibody and radioiodinated protein A. Analytical Biochemistry, 1981;112(2):195–203.
• Bradford MM. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Analytical Biochemistry, 1976;72:248–254.
• Shapiro AL, Viñuela E, Maizel JV. Molecular weight estimation of polypeptide chains by electrophoresis in SDS-polyacrylamide gels. Biochemical and Biophysical Research Communications, 1967;28(5):815–820.
• Assay Genie Western Blot Protocol & Troubleshooting Guide

Frequently asked questions