Sulfate binding protein active site

Protein concentrations do not necessarily accurately estimate active sites, even when proteins are pure based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Typically, protein concentrations yield upper estimates of active site concentrations. The best method to determine active sites is based on an activity, such as inhibitor binding. Therefore, tight-binding inhibitors are often the best method to determine the active site concentration of an enzyme. As a general rule, the best estimates of active site concentration come when the maximal enzyme concentration used in the assay is at least five- to 10-fold greater than the inhibitor IC50 value. 

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