Studies of chemical recognition in biology were initiated about half a
century ago with the flrst kinetic data obtained on enzyme catalysis and
inhibition. They led to a rather static representation of the
recognition process illustrated by the lock and key model that still
continues to influence our overall image of recognition and its
specificity. In several cases, crystallographic studies of
enzyme-substrate complexes have supported this model. Indeed, in a
crystallized ligand-enzyme complex, a close fltting is observed between
the active center of the enzyme and the functional groups of the ligand.
How- ever, this does not necessarily result from a direct recognition
process between rigid structures, but may result from a progressive
adaptation during which the initial struc- tures of the enzyme and the
ligand are modified (induced-flt mechanism). Recently, a great deal of
work has been devoted to the study of recognition in more complex
systems such as the replication or the translation machin ries; clearly,
the extraordinary precision of such systems cannot be explained solely
in terms of physical matching between enzymes and their substrates. This
has led to a noticeable change of perspective in these areas. As a
result of the new kinetic viewpoint, one rather focuses on the
time-course of the processes, on the kinetic balance between steps of
the reaction, on the energy-accuracy relationships and on the strategies
which permit the achievement of high precision using relatively
error-prone components in an appropriate dynamic interplay.