Abzymes - Abzymes are antibodies that catalyze specific chemical reactions, i.e. function as enzymes. Antibodies by definition have evolved to recognise and bind to the ground states of the molecules they are specific to. In contrast, enzymes have binding sites that preferentially bind to the transition state of their substrate molecules.

For this reason abzymes are not produced naturally. A catalytic antibody is produced in response to molecules that have a structure similar to the proposed expected transition state of the substrate of the reaction to catalyse which the antibody is sought.

The fact that such catalytic antibodies are in fact produced is the strongest evidence in support of the transition theory of enzyme action.