Specific binding of a ligand to a receptor is a key step in a variety of biological
processes, such as immune reactions, enzyme cascades, or intracellular
transport processes. The ligand–receptor terminology implies that the receptor
molecule is significantly larger than the ligand, and the term “bioactive
conformation” usually characterizes the conformation of a ligand when it is
bound to a receptor. In a more general sense, bioactive conformation applies
to any molecule in a biologically relevant bound state regardless of size considerations.
Most of the contributions to this book address ligands that are much
smaller than their receptors.