Protein and nucleic bands can be extracted from either polyacrylamide or agarose gels by electro-elution of the molecules. To facilitate this method, Novagen (EMD Biosciences) offers the D-Tube Dialyzer Kit. The thick plastic tubes found in the kit contain a hollow center for the sample, with two dialysis membrane windows directly opposite to each other. As with all membranes, they are extremely fragile and are prone to minute punctures if the user is not careful. Otherwise, the rest of the system is quite robust and hassle-free. We were successful at extracting approximately 5 ug of a 60 KDa protein from gradient polyacrylamide gels (4-20%) by applying a constant voltage of 114 V for 1 hr and 45 min. Although the company claims 60-85% protein recovery, our results suggest that recovery is toward the lower end of this range. This factor is problematic for both low abundant proteins and dilute samples that require sample concentration prior to electrophoresis. The minimum prescribed amount of protein prior to extraction is 0.5 ug, but we speculate that the yield for such a starting amount will be quite poor. There is no advantage to using larger wells as the extraction efficiencies decrease with bands larger than 1 cm x 5 cm. A minimum of 800 ul is needed to ensure that the bands are completely immersed in SDS Running buffer, but this will result in a rather large volume of diluted protein. If a larger gel slice is required, upgrading to the Maxi kit is the best option.
An added feature for this product is its extreme ease of use for dialysis. Each kit comes with a floating tube holder (although any wide bore floating rack will do). We found this dialysis format extremely user friendly as it does not require syringes, tubing, ties, as would be needed for other protocols. Addition and extraction of sample solutions was quick and easy. Dialysis to remove residual SDS immediately following electro-elution was also possible (not all SDS is eliminated during electro-elution), but the tubes should be carefully handled to prevent membrane puncture. This is the only viable extended use application that we found for this otherwise single-use format. We have not tried to use the tubes for nucleic acids extractions since other kits are already available in the lab for this purpose. However, both companies do claim the standard greater than 90% (97% claimed by Novagen) recovery of nucleic acids.
The D-Tube Dialyzer Kit offers protein retention membranes with 3.5 , 6-8 and 12.4 KDa MWCO,. Novagen also offers a Mini format (10 to 250 ul volumes) with 6-8 KDa and 12.4 KDa MWCO. The kit comes with a TCA and a Mass Spectrometry compatible buffer along with the electrophoresis tube tray and there are 10 tubes per kit.
In summary, this is a versatile and relatively inexpensive product that will always find use in any molecular biology laboratory. At present we find few limitations for this product’s intended use and as such, if your experiments routinely utilize dialysis and protein isolation, this product will fit your bill.
Rhoel Dinglasan, Ph.D., M.P.H.
Postdoctoral Fellow
Johns Hopkins Bloomberg School of Public Health