About 30 years ago all known enzymes were each allotted a formal name and number (main category 1-6) that is definitive for that enzyme (although usually including isoenzymes with the same bioconversion result). A mild problem arose in more recent years when a few particular bacterial enzymes were found to possess dual specificity and function, each manifest by one protein domain (the result of gene fusion it would seem). Now, this can be deliberately arranged by modular addition of extra activities : such as oxidoreductase ability (category 1 activity) added to a simple hydrolase enzyme (category 3 activity enzyme). Multiple catalysis by proteins (and other polymers) will become the tailor-made (or off the peg) choice of bioconversion-chemists in the twenty-first century : biomimetics may be built into such proteins as an optimal extra.