  Conformational changes are observed in many enzymes, but their role in
catalysis is highly controversial. Here we present a theoretical model that
illustrates how rigid catalysts can be fundamentally limited and how a
conformational change induced by substrate binding can overcome this
limitation, ultimately enabling barrier-free catalysis. The model is
deliberately minimal, but the principle it illustrates is general and
consistent with unique features of proteins as well as with previous informal
proposals to explain the superiority of enzymes over other classes of
catalysts. Implementing the discriminative switch suggested by the model could
help overcome limitations currently encountered in the design of artificial
catalysts.
