<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>Ligand Binding is the tight and specific (high affinity) interaction between a small molecule (typically) and a macromolecule (usually protein) that ordinarily results in modification of its function, e.g., antigen-antibody binding, hormone- or neurotransmitter-receptor binding.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>