Loading Control Antibodies
Reliable western blot normalisation starts with the right loading control. St John's Laboratory offers a broad range of antibodies targeting housekeeping proteins across cytosolic, nuclear and organelle fractions, with monoclonal and polyclonal options and multi-species reactivity across up to 17 species.
Browse All Loading Control Antibodies
What Are Loading Control Antibodies?
Purpose and Principle
Loading control antibodies target proteins with consistently high, ubiquitous expression across most cell types, tissues and species. By detecting one of these housekeeping proteins on the same blot as your target, you can confirm that any differences in band intensity between lanes reflect genuine biological changes rather than inconsistencies in sample preparation, protein quantification or gel transfer.
They are particularly important when comparing samples across different treatment conditions, time points or cell lines, where even small variations in loading can otherwise be misinterpreted as meaningful changes.
The most widely used loading controls target cytosolic proteins such as GAPDH, Beta-Actin and Tubulin. For nuclear fractions, Histone H3 and Lamin A/C are commonly used. For membrane and mitochondrial fractions, Na/K-ATPase and COX IV serve as appropriate controls.
Choosing the Right Loading Control
Three key criteria should guide your selection. The control protein's expression level should remain stable under your experimental conditions. Its molecular weight should be sufficiently different from your target protein to allow clear separation on the same gel. And its subcellular localisation should match the fraction you are analysing.
- Use GAPDH or Beta-Actin for whole cell or cytoplasmic lysates (37 and 42 kDa respectively)
- Use Tubulin when your target is not near 50 kDa
- Use Histone H3 or Lamin A/C for nuclear fractions (17 and 74 kDa)
- Avoid GAPDH in hypoxia or metabolic studies where its expression may be altered
- Avoid PCNA in experiments involving DNA damage or cell cycle arrest
- Consider Vimentin as an intermediate filament control in mesenchymal cell types
Why Choose Loading Control Antibodies from St John's Laboratory?
Monoclonal and Polyclonal Options
Both monoclonal and polyclonal formats are available for key targets. Monoclonals offer high specificity and lot-to-lot consistency; polyclonals provide broad multi-epitope coverage for robust signal detection.
Broad Species Reactivity
Most antibodies in the STJ140 goat polyclonal range are reactive across up to 17 species, including human, mouse, rat, bovine, porcine, rabbit, sheep and simian, making them suitable for a wide range of model organisms.
Multiple Subcellular Compartments
Coverage across cytosolic, nuclear envelope and cytoskeletal fractions, so you can normalise appropriately regardless of which cellular compartment your target protein resides in.
Comprehensive Datasheets
Each antibody is supplied with a datasheet. Where available, representative western blot images, dilution recommendations and related reagents are included to support your assay setup.
Loading Control Selection Guide
Select a loading control whose molecular weight is at least 5 kDa from your protein of interest, and whose expression is known to be stable under your experimental conditions. This table summarises the most commonly used targets.
| Target | Fraction | MW | Notes | Browse |
|---|---|---|---|---|
| GAPDH | Cytosolic | 37 kDa | Most widely used; avoid in hypoxia, diabetes or metabolic studies where expression may vary | Browse |
| Beta-Actin (ACTB) | Cytosolic | 42 kDa | Highly conserved; not suitable for studies of cell growth or cytoskeletal reorganisation | Browse |
| Alpha-Tubulin (TUBA) | Cytosolic | 50 kDa | Good alternative when target is not near 50 kDa; may vary with antimitotic drug treatment | Browse |
| Beta-Tubulin (TUBB) | Cytosolic | 50 kDa | Pairs with alpha-tubulin; reduced expression in adipose tissue | Browse |
| Vimentin (VIM) | Cytosolic | 54 kDa | Intermediate filament marker; useful in mesenchymal, fibroblast and cancer cell studies | Browse |
| Lamin A/C (LMNA) | Nuclear | 74 kDa | Nuclear envelope marker; useful when studying nuclear structure or laminopathies | Browse |
| PCNA | Nuclear | 29 kDa | DNA replication marker; not suitable for non-proliferating cells or DNA damage experiments | Browse |
| Na/K-ATPase (ATP1A1) | Membrane | 113 kDa | Plasma membrane control; useful for membrane fraction validation | Browse |
| COX IV | Mitochondrial | 17 kDa | Inner mitochondrial membrane control for mitochondrial fraction experiments | Browse |
Cytosolic Loading Controls
The most widely used loading controls for whole cell lysates and cytoplasmic fractions. GAPDH, Beta-Actin and Tubulin are all abundant, highly conserved proteins whose expression is stable across most standard experimental conditions. Please check individual datasheets for confirmed applications and species reactivity per product.
GAPDH Antibodies
37 kDa · Cytosolic · Most widely used loading control for western blot
GAPDH: Also Available with DyLight Conjugates
For secondary-free fluorescence western blotting, GAPDH is available pre-conjugated to DyLight 405, 488, 550 and 633. This simplifies multiplex blotting workflows by removing the secondary antibody incubation step and reducing non-specific background.
Beta-Actin (ACTB) Antibodies
42 kDa · Cytosolic · One of the most widely cited loading controls in the literature
Tubulin Antibodies
50 kDa · Cytosolic · Alpha and beta isoforms available for cytoskeletal fraction normalisation
Vimentin (VIM)
54 kDa · Cytoskeletal · Intermediate filament control for mesenchymal and stromal cell types
Nuclear Loading Controls
When working with nuclear extracts or subcellular fractionation experiments, cytosolic controls such as GAPDH and Actin are not appropriate. Lamin A/C marks the nuclear envelope and is a suitable control at 74 kDa, well-separated from most cytosolic housekeeping proteins. Histone H3 (17 kDa) is the classical nuclear control but should be avoided in cell cycle studies where histone levels change with DNA replication.
Lamin A/C (LMNA)
74 kDa · Nuclear envelope · Useful at a distinct molecular weight from most cytosolic targets
PCNA
29 kDa · Nuclear · For proliferating cell studies; not suitable for DNA damage or cell cycle arrest experiments
More Nuclear and Organelle Controls in Our Full Catalogue
Our full loading control range includes Histone H3 for nuclear fractions, PCNA for proliferating cell studies, Na/K-ATPase for plasma membrane fractions, and COX IV as a mitochondrial marker. These are available across multiple clonalities and conjugation formats.
Monoclonal, Polyclonal and Conjugated Formats
Unconjugated Primary Antibodies
Used with a compatible secondary antibody for detection. Gives flexibility across different secondary formats and detection systems including ECL, fluorescence and chromogenic methods.
HRP-Conjugated Options
HRP-conjugated loading control antibodies allow direct detection without a secondary antibody step, reducing background and simplifying your western blot workflow.
DyLight Fluorescent Conjugates
Pre-conjugated to DyLight 405, 488, 550 and 633. Suitable for multiplexed fluorescence western blotting alongside a target antibody in a different channel, without secondary antibody cross-reactivity issues.
High Lot-to-Lot Consistency
Especially important for loading controls used repeatedly across long-running experiments. Monoclonal formats offer the highest consistency, and are available for key targets including GAPDH and Beta-Actin.
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Western Blot & Loading Control Resources
Loading Control Antibody Guide
In-depth background on loading control selection, subcellular localisation and common pitfalls to avoid in western blot normalisation.
Western Blot Protocol
Step-by-step protocol covering sample preparation, SDS-PAGE, transfer, blocking and detection.
Western Blot Troubleshooting
Diagnose and fix common issues including high background, weak signal, incorrect band size and uneven loading.
Browse the Full Loading Control Range
Unconjugated, HRP and DyLight-conjugated antibodies for GAPDH, Actin, Tubulin, Histone H3, PCNA, Lamin, Na/K-ATPase and more.
View All Loading Control Antibodies