~8000 units/mg. One unit cleaves 1 nmol of the caspase substrate YVAD-pNA per hour at 37°C in a reaction solution containing 50 mM HEPES, pH 7.2, 50 mM NaCl, 0.1% CHAPS, 10mM EDTA, 5% glycerol and 10 mM DTT.
Caspase-1 (also known as ICE, Interleulin-1- Converting Enzyme) is the prototypical member of the caspase family of cysteine proteases. Caspase-1 exists in cells as an inactive 45 kDa pro-enzyme. The pro-enzyme is matured by proteolysis to yield large (20 kDa) and small (10 kDa) subunits. The active enzyme is a heterotetramer consisting of two large and two small subunits. To date the mechanism of regulation of caspase-1 activation is complex and poorly understood. In THP-1 cells, a large proportion of the caspase-1 is present in the inactive pro-enzyme form.