Complete the text below Catalytic antibodies have a number of advantages for the organic chemist over enzymes. Enzymes have significant limitations in synthesis. First, they only on compounds similar to the substrate and then with rather low affinities. Second, there are many for which there is no known enzyme catalyst. In both situation, abzymes can be of benefit to the synthetic chemist because they are “programmable'”. The range of reactions that can be catalyzed by appears to be limited only by sufficient knowledge of the transition state for any given reaction and the possibility of or an appropriately stable transition state analogue. Perhaps the best example of this to date has been the production of a Diels-Alderase antibody. The reaction is one of the most useful carbon-carbon bond-forming processes in chemistry, for which there are no known catalyst.