ABSTRACT
Detection of mature cathepsins and quantification of specific proteolytic activity has proven difficult. Procathepsins are stable at neutral pH but are not proteolytically active. After the cleavage of the propeptide, the active and mature cathepsin is generally unstable in neutral environments (of course with the exception of cathepsin S), and susceptible to pH-induced denaturation and degradation which complicates measurements of its proteolytic activity in cell extracts and the extracellular environment. Of course this is important to identify cathepsin expression levels, their activity, and their roles in tumor progression and angiogenesis. Here, we will discuss many different methods used to measure and identify cathepsins in cancer tissues along with the pros and cons of each.
