PageRuler™ Unstained Broad Range Protein Ladder, 8 x 250 μL - FAQs

Here are possible causes and solutions:

- Ladder was boiled: Discard boiled aliquot.
- Too much volume of ladder used: Add less volume or dilute the ladder in protein loading buffer prior to use.
- DTT oxidation in storage buffer: Add freshly prepared DTT solution to a final concentration of 100 mM.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

- Decrease voltage, current or length of transfer time
- Make sure that the methanol concentration in the transfer buffer is proper; use a methanol concentration of 10-20% methanol removes the SDS from SDS-protein complexes and improves the binding of protein to the membrane.
- Make sure that the SDS concentration (if added) in the transfer buffer is proper, don't use more than 0.02-0.04% SDS. Using too much SDS can prevent binding of proteins to the membrane.
- Check the pore size of the membrane and the size of the target protein. Proteins smaller than 10 kDa will easily pass through a 0.45 µm pore size membrane. If proteins smaller than 10 kDa are of interest, it would be better to use a 0.2 µm pore size membrane.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

- Increase voltage, current or length of time for transfer
- SDS in the gel and in the SDS-protein complexes promotes elution of the protein from the gels but inhibits binding of the protein to membranes. This inhibition is higher for nitrocellulose than for PVDF. For proteins that are difficult to elute from the gel such as large molecular weight proteins, a small amount of SDS may be added to the transfer buffer to improve transfer. We recommend pre-equilibrating the gel in 2X Transfer buffer (without methanol) containing 0.02-0.04% SDS for 10 minutes before assembling the sandwich and then transferring using 1X transfer buffer containing 10% methanol and 0.01%SDS.
- Methanol removes the SDS from SDS-protein complexes and improves the binding of protein to the membrane, but has some negative effects on the gel itself, leading to a decrease in transfer efficiency. It may cause a reduction in pore size, precipitation of some proteins, and some basic proteins to become positively charged or neutral. Make sure that the methanol concentration in the transfer buffer is not more than 10-20% and that high-quality, analytical grade methanol is used.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

Pre-stained standards have a dye that is covalently bound to each protein that will result in the standard migrating differently in different buffer systems (i.e., different gels). As a result, using a pre-stained standard for molecular weight estimation will only give the apparent molecular weight of the protein. Pre-stained standards may be used for molecular weight approximation, confirming gel migration and estimating blotting efficiency but for accurate molecular weight estimation, an unstained standard should be used.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

- While loading, take care to make sure that there is no cross-contamination from adjacent sample lanes.
- Make sure that the correct amount of standard is loaded per lane. Loading too much protein can result in extra bands and this is a problem especially with silver-stained gels.
- Improper storage of the standard or repeated freeze/thawing can result in protein degradation.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

Here are some suggestions:

- Make sure that the correct amount of standard is loaded per lane. Loading too much protein can cause smearing and this is a problem especially with silver stained gels.
- Bands will not be as well resolved in low percentage gels. Try using a higher percentage gel.
- If the bands look smeary and non-distinct after a western transfer/detection, this may be due to the antibody being too concentrated. Follow the manufacturer's recommended dilution or determine the optimal antibody concentration by dot-blotting.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

Here are some suggestions:

- Check the gel type/percentage of the gel that was used. Depending on the gel type and/or percentage, all the bands may not be seen. For example, the smallest bands of the protein standard may not resolve on a very low percentage gel whereas the higher molecular weight bands may not resolve on a high percentage gel.
- Check the expiration date on the protein standard. Expired lots may result in faded or missing bands due to protein degradation.
- Check the storage conditions for the protein standard. Improper storage conditions will compromise the stability of the proteins in the standard.
- Make sure that the protein standard was not heated/boiled prior to loading on the gel. Our protein standards are ready to load and we do not recommend heating/boiling them as this may cause degradation of proteins in the standard.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

The PageRuler Unstained Protein Ladder, PageRuler Unstained Broad Range Protein Ladder, and PageRuler Unstained Low Range Protein Ladder contain recombinant prokaryotic proteins and do not contain any animal-derived proteins.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

The proteins in the different PageRuler Unstained Protein Ladders (except for the 3.4 and 5 kDa peptides in the PageRuler Unstained Low Range Protein Ladder and the PageRuler Unstained Protein Ladder, and the 5 kDa peptide in the PageRuler Unstained Broad Range Protein Ladder) contain an integral Strep-tag II Sequence and may be detected on western blots using Strep-Tactin Conjugates.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

The PageRuler Unstained Broad Range Protein Ladder is a mixture of eleven recombinant, highly purified proteins ranging from 5 kDa to 250 kDa. For easy reference, the 100 kDa, 50 kDa and 20 kDa protein bands have greater intensity than the other proteins in the ladder.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.

We recommend storing the PageRuler Unstained Protein Ladders at -20 degrees C where they are stable for a year.

Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.