ON THE MASKING OF SIGNALS ON IMMUNOBLOTS BY CELLULAR PROTEINS

When determining the concentration of a particular protein in a cell e xtract, or when comparing the amount of a protein in different samples , it is a common practice to use specific antibodies in immunoblotting to compare the samples side by side with known amounts of purified pr otein. Here we show that with many antibodies, in particular monoclona l antibodies, the sensitivity of detecting the cognate antigen on immu noblots can be significantly reduced when the antigen is in a mixture with other cellular proteins. The signals on the immunoblots are maske d by other endogenous proteins in the cell lysate, making the amount o f the protein on the immunoblot appear to be less than the actual amou nt, thus invalidating direct comparison with purified protein.