400 units/mg. One unit is the enzyme activity that cleaves 1 nmol of the caspase substrate LEHD-pNA per hour at 37°C in a reaction solution containing 50 mM Hepes, pH 7.2, 50 mM NaCl, 0.1% Chaps, 10 mM EDTA, 5% Glycerol, and 10 mM DTT.
Active enzyme was expressed in E. coli. The expressed caspase-9 spontaneously undergoes autoprocessing to yield the subunits characteristic of the native enzyme. One unit of rhCaspase-9 is the enzyme activity that cleaves 1 nmol of substrate Ac-LEHD-pNA per hour at 37°C at standard substrate concentrations. In combination with caspase-9 activity assays, the active rhCaspase-9 is useful in screening caspase inhibitors for pharmaceutical applications. The enzyme is also useful in studying enzyme regulation, determining target substrates and as a positive control in caspase-9 assays.