How does choice of blocking protein - nonfat dry milk vs bovine serum albumen (BSA) - affect your Western Blot (WB) results?
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Transcript:
- What protein should I use to block a transfer membrane for a western blot? My name is Srikanth, I'm a product scientist at Cell Signaling Technology, and this is CST Tech Tips.
In regards to western blotting, a common question we always get is, what should I use, milk or BSA to block? So the purpose of blocking step is to reduce the amount of background due to non-specific bonding. Now BSA is only made up of one protein, BSA at 60 kDa, whereas milk is made up of many proteins, all of various sizes. So you get a much better chance to reduce more of the background banding.
We recommend that you use 5% milk in TBST, shaken for one hour at room temperature, to block all of our non-conjugate primary antibodies. This includes phospho-specific and total antibodies. Now I can already hear the clicking, comments, and hashtags, asking about "what about the phosphatases in milk?" Well, there are some papers out there that discourage you from using milk for phospho signal.
Let me address that by saying that in all of our in-house testings, we don't see any of these issues. CST scientists run so many westerns that we end up making milk once, at least once a day, sometimes multiple times a day. Now, if your milk buffer goes unused for a week, two weeks, even longer, that increases your chances of phosphatases affecting your signal. But again, we don't see any of these effects, because we use milk buffer fresh on a daily basis.
These are images of product number 13038, tested on lysates made from 3T3 cells treated with PDGF. The only difference between the blots is that one membrane is blocked in milk, and the other membrane is blocked in BSA. Clearly, the membrane blocked in BSA has a much higher background. Yet phospho signal is still strong and clean with the membrane blocked in milk.
So after the membrane has been blocked, please refer to the product's specific data sheet for the recommended antibody dilution buffer. It's either gonna be milk or BSA, depending on the specific antibody.
I hope this has been helpful. For full application specific protocols, they're available on cellsignal.com on specific product page. If you have any other questions, please feel free to contact any of the scientists at CST at cellsignal.com.... For more CST Tech Tip videos, please subscribe to our RU-vid page. Good luck with your experiments. And we'll see you next time, thanks.
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29 авг 2024