Studies on the inactivation of soluble and immobilized papain by the ascorbic acid-Cu2+ system:: a model to propose the effect of free radicals on membrane-bound enzymes in vivo

Free radicals have been suggested to be widely implicated as the species responsible for harmful biological processes, such as aging, carcinogenesis and numerous other diseases. The mechanism of biological damage produced in such processes has been investigated in a wide variety of systems, including studies on proteins, enzymes, nucleic acids and carbohydrates. In the present study we selected an ascorbic acid-transition-metal ion (ASA-Cu2+) system in order to understand the mechanism of soluble and membrane-bound enzyme inactivation by generating free radicals. Papain, a thiol protease, was immobilized on an immobilized-metal-ion carrier and used as a model to examine the inactivation behaviour of membrane-bound enzymes. A comparison was made between the inactivation of soluble and immobilized papain by free radicals, and the potential of different radical scavengers to prevent the inactivation of enzyme was examined.