1. They are secreted as proenzymes and require extracellular activation. 2. These are secreted in an inactive form called ( termed zymogens or proenzymes ). 3. This type of inactive precursor to an enzyme is known as a zymogen or proenzyme . 4. Enzyme precursors are called zymogens or proenzymes . 5. There is currently no other known modifications necessary to activate the proenzyme and enable catalytic activity. 6. In both cases inactive proenzymes such as hemocyanin, tyrosinase, and catcholoxidase must be activated first. 7. Most MMP's are secreted as inactive proenzymes which are activated when cleaved by extracellular proteinases. 8. Caspases exist as inactive proenzymes composed of a prodomain, a large protease Fas and various apoptotic stimuli. 9. When these proenzymes reach the lumen of the tract, a factor specific to a particular proenzyme will activate it. 10. When these proenzymes reach the lumen of the tract, a factor specific to a particular proenzyme will activate it.
