Invitrogen™ Novex™ pH 3-7 IEF Buffer Kit, Includes LC5300, LC5370, LC5371

There are several reasons why streaking may occur.

(1) Sample is not completely solubilized prior to application.

(2) Sample is poorly soluble in rehydration solution.

(3) Non-protein impurities in the sample can interfere with IEF, causing horizontal streaking in the final 2-D result, particularly toward the acidic side of the gel.

(4) Ionic impurities are present in sample.

(5) Ionic detergent is present in sample.

(6) Sample load is too high.

(7) Underfocusing. Focusing time was not long enough to achieve steady state focusing.

(8) Overfocusing. Extended focusing times (over 100,000 Vh) may result in electroendosmotic water and protein movement, which can produce horizontal smearing.

What should be done?

(1) Be sure that the sample is completely and stably solubilized. Note: Repeated precipitation-resolubilization cycles produce or increase horizontal streaking.

(2) Increase the concentration of the solubilizing components in the rehydration solution.

(3) Modify sample preparation to limit these contaminants or dialyze protein.

(4) Reduce salt concentration to below 10 mM by dilution or desalt the sample by dialysis. Precipitation with TCA and acetone and subsequent resuspension is another effective desalting technique that removes lipids, nucleotides and other small molecules.
Note: Specific and non-specific losses of proteins can occur with dialysis, gel chromatography, and precipitation/resuspension of samples. If the sample preparation cannot be modified, the effect of ionic impurities can be reduced by modifying the IEF protocol. Limit the voltage to 100-150 V for 2 hours, then resume a normal voltage step program. This pre-step allows the ions in the sample to move to the ends of the IPG strip.

(5) If the ionic detergent SDS is used in sample preparation, the final concentration must not exceed 0.25% after dilution into the rehydration solution. Additionally, the concentration of the non-ionic detergent present must be at least 8 times higher than the concentration of any ionic detergent to ensure complete removal of SDS from the proteins.

(6) Extend focusing time. Load less sample.

(7) Prolong focusing time.

(8) Reduce focusing time.

Yes, the fix serves two purposes: it fixes the sample in the IEF gel and it helps to remove gel background.

If you do not use the fixing solution, the background on the gels will be high and detection will be less sensitive.

High background is caused by ampholytes remaining in the gel.

Yes, you can use just arginine (either form of arginine) as long as the arginine free base form is used and not the hydrochloric form. Note that the lysine used to make the mixed buffer should be free base lysine; free acid lysine should not be used as a substitute. The reason for adding basic amino acids to the cathode buffer is to increase the ionic strength of the buffer in order to fortify the basic end.