Degradation of target proteins by proteases is a constant danger when working with and analyzing proteins. Inhibition of intracellular proteases is necessary to maintain and preserve cellular protein integrity during cell lysis, protein extraction and subsequent analyses. This goal can be achieved by the time consuming process of mixing aliquots of different protease inhibitors (aprotinin, leupeptin, pepstatin, etc), some of which are toxic. However, ready to use commercial protease inhibitor cocktails are a convenient and economical alternative.
The HALT Protease Inhibitor Cocktail from Pierce Biotechnology is an easy to use, convenient protease inhibitor cocktail that inhibits a wide variety of cellular proteases. This includes serine and cystine proteases, calpain proteases and, when EDTA is added, metalloproteases. Although it is one of the most comprehensive inhibitors on the market, pepstatin needs to be added if inhibition of aspartic proteases is required. It comes in 2 forms: with EDTA and EDTA-free for instances when protein activity may be affected by the chelation of divalent cations by EDTA.
HALT is extremely easy to use and is compatible with cell lysates produced by various methods. It is supplied at 100X concentration and stored at 40C. It should be warmed to room temperature before use. I have generally used it at 1X concentration, but it can be used at 2X-3X for increased activity. It is very economical as you only add the amount required to the lysis buffer, and any leftover lysis buffer-HALT mixture can be stored up to 15 weeks at -200C. Although I have personally only used it for mammalian cells, according to Pierce it can be used for tissue, bacteria, yeast and plants.
In summary, I would have to say that I consistently get excellent results with HALT. It is safe, easy to use and very effective and I would have no problems recommending it to anyone who is performing protein purification.
Onikepe Adegbola
Graduate student
Johns Hopkins University School of Medicine