At times, it is necessary to elute proteins in buffers that are not very conducive to some down stream applications. Dialysis is often the next (and most-dreaded) step. I used to avoid dialysis whenever I could because it was such a temperamental procedure. Protein yield and sample volume were always problems. I would do everything I possibly could to elute my protein of interest with a buffer compatible with any downstream uses. Although I still try to keep the number of different buffers used in protein isolation and purification experiments to a minimum, I now feel more comfortable eluting proteins with a more appropriate elution buffer and then dialyzing my sample using Pierce Biotechnology’s Slide-A-Lyzer dialysis cassettes.
Pierce’s Slide-A-Lyzer dialysis products can dialyze a wide range of volumes (100 ul – 30 mL) with your choice of several different molecular weight cut offs (MWCO). The dialysis kit comes with both cassettes and cassette buoys.
Overall, I found the process of using these cassettes to be quite easy. After hydrating the membrane for 30 seconds in dialysis buffer, I added the sample to the cassette with a syringe and needle, taking care not to puncture or touch the membrane with the needle. There are four ports (one at each corner) for sample addition and removal. After the sample had been added, I used the syringe to remove any air from the cassette. Once the cassette was loaded, I fitted it into a buoy and placed it in a beaker with 300 mL of the solution I wanted to dialyze against. After several hours and a couple of solution changes, I removed my sample from the cassette. This is essentially a reversal of the addition procedure.
When using the Slide-A-Lyzer, there are a few things to keep in mind: keep the bevel of the needle 90° to the membranes so that you won’t inadvertently suck the membrane to the needle, and second, stick the needle far enough into the cassette so that you can only see the bevel. This will reduce your chances of touching or puncturing a hole in the membranes.
Although this product is easy to use, it is not necessarily the silver bullet that will solve all of your dialysis problems. The first couple of times I used it I found that post-dialysis protein concentrations were severely reduced. However, I found that the addition of a small amount of SDS largely solved that problem. Overall, I have been pleased with this product and continue to use it.
J.Jason Clark
Research Assistant
University of Iowa