Total Protein Stain as an Internal Loading Control

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Using a total protein stain to detect the total protein in each lane of your gel or blot is becoming more popular. Total protein staining is a direct measure of the total amount of sample protein in each lane. For each lane, the sum of all the signal intensities of all the proteins in the lane is used for normalization.

This more direct approach may increase the accuracy of normalization. Unlike housekeeping proteins, total protein staining does not require validation for each experimental context.

A total protein stain should produce a linear increase in signal intensity in response to increasing protein concentration. It should also correct for variation at all points in the Western blot process, including gel loading and transfer to membrane. It must be compatible with downstream immunodetection of your blot. You should make sure that the signal intensity of the total protein stain is moderate, without saturation or low signal-to-noise ratios.

REVERT™ Total Protein Stain provides linear, proportional signal across a broad range of sample concentrations.

REVERT Total Protein Stain

Learn more about total protein controls in the full paper on normalization: Western Blot Normalization: Challenges and Considerations for Quantitative Analysis

Housekeeping Proteins as Internal Loading Controls

Normalization Webinar InvitationFor more information on Western blot normalization, watch these webinars:

Housekeeping proteins such as tubulin, actin, and GAPDH are often used to normalize. In the past, researchers assumed that these proteins were constant in every cell type, because these proteins maintain basic cellular function. Housekeeping proteins are acceptable loading controls if expression is stable, but expression of these proteins can vary depending on your cellular context.

Housekeeping proteins won’t effectively normalize in every experiment, but that doesn’t mean they won’t work for any experiment. If you choose to use a housekeeping protein as your normalization strategy, be sure to validate it to confirm stable expression for your experimental context. As cell types, tissue types, disease states, and experimental treatments change, your internal loading control should remain constant.

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Here are some things to keep in mind:

  • Gene expression levels do not reliably predict protein abundance. Just because mRNA levels are constant, this does not mean protein levels will be similarly constant.
  • Biological factors, like tissue type, growth conditions, stage of development, and disease, may influence expression of housekeeping proteins. Without constant expression, housekeeping proteins are an unreliable way to normalize.
  • Housekeeping proteins are typically very abundant. The resulting strong bands freque[marketo-fat form=”1644″]ntly cause signal saturation, which reduces the accuracy of detection.

If you have validated that your housekeeping proteins are constant across all your experimental treatments, you can use them as a reliable loading control. Actin, tubulin, and COX IV primary antibodies can be used for two-color normalization.

Find out more about housekeeping proteins as internal loading controls in Western Blot Normalization: Challenges and Considerations for Quantitative Analysis.