Cathepsin zymography is a technique for quantifying enzymatic activity of the cathepsin family of cysteine proteases. It is based on SDS-PAGE whereby samples tested for cathepsin activity are loaded into a polyacrylamide gel and then separated by molecular weight. Gelatin is embedded in the gel itself, providing a substrate for the enzymes to hydrolyze.
While the proform of cathepsins are generally stable, once activated, proteases such as cathepsin K are vulnerable to inactivation in neutral pH environments. This loss of activity complicates detection of these enzymes. Zymography, through its high sensitivity and multiplex nature allows for the simultaneous distinction between multiple cathepsins. Very small amounts of enzymatic activity can be elucidated and is capable of resolving a femtomole of cathepsin K activity.