Production of Artificial Semi Synthetic Oxido Reductases - Flavo Enzymes - Artificial oxido reductases can be prepared by covalently attaching redoxactive prosthetic groups to existing sites. Linking of 10-methyilsoalloxazine derivatives (as redox-active groups) to specific sites of several proteins has been achieved. The efficiency of these semisynthetic enzymes (e.g. flavopapain) compares favourably with that of naturally occurring flavoenzymes.