Lysozyme is said to be a good protein with which to set up a standard curve for the Bradford protein assay. We have tried using it, but after a few minutes a fine precipitate starts to form and it seems to be affecting our assay reproducibility. Has anybody else had a similar experience?
I have seen examples of proteins precipitating in the Bradford assay. You could switch to the BCA assay, or some other protein assay, or you could switch to a different standard. I use bovine serum albumin.
Thanks, I just wanted to confirm that we are not the only ones who has found this. We will probably revert back to using BSA as standard, as we have had good results with this previously.
I agree with Adam. Lysozyme has a pI of ~10 which makes it insoluble at the low pH used in the Bradford assay.
Plus the BCA assay is easier to use and is more stable.
@Mangal, you are correct. Most proteins least soluble at their pI.
But when extreme pH changes are introduced, they can denature. As Neill's observations about lysozyme precipitation demonstrate.
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