If you buy primary antibodies from different places, you may have noticed that many companies list the size of their products in micrograms per ml (i.e., by weight). You may have also noticed that CST does not - CST antibodies are listed by performance (e.g., 10 western blots) instead.
So what’s the difference? Well, in some cases, companies do a partial purification to increase the yield of total protein. This approach increases total protein concentration without affecting the percentage of the protein mass that is specific to the intended target. In other words, you might be excited to receive an antibody at a concentration of 1 mg/ml. However, you might be less excited to find that the target specific antibody only comprises a small fraction of the total protein. The remainder is a mix of non-specific antibodies and assorted serum proteins.
In contrast, CST uses a purification protocol that involves a Protein A chromatography step, which removes all non-antibody proteins from the source material. This step is followed by a peptide affinity purification step to isolate the antibody species specific to the target of interest. This method ensures that the protein mass is predominately target antibody. And, while it is true that the concentration of the pure antibody in weight (μg) may vary from product to product and from lot-to-lot, each lot is tested to ensure antibody performance is similar or superior from one lot to the next.
Thus, even if the protein concentration of the final purification product is low, the overall performance will be consistently strong.
The moral of the story is “buyer beware.” Concentration may not give you the best indication of how well the product will perform; and, at the end of the day performance is what really matters . . . which is why CST prefers to supply antibodies by performance and not by weight.
Want to know more about how CST generates high performance antibodies?