The specific activity of the caspase enzymes used was determined with a standard curve using free AFC and the Ac-VEID-AFC or Ac-DEVD-AFC substrate for caspase-6 and caspases -3 and -7, respectively. The resulting specific activities were: 11.7 nmol Ac-VEID-AFC/min/mmol caspase-6, 13.7 nmol Ac-DEVD-AFC/min/mmol caspase-3 and 9.9 nmol Ac-DEVD-AFC/min/mmol caspase-7.