XmlmmCIF equivalent: struct_site Data items in the STRUCT_SITE category record details about portions of structure that contribute to certain structurally relevant sites (e.g. active sites, substrate-binding subsites, metal-coordination sites). XmlmmCIF equivalent: struct_site/details A description of special aspects of the structural site. XmlmmCIF equivalent: struct_site/pdbx_num_residues Number of residues in the site. XmlmmCIF equivalent: struct_site/id The value of _struct_site.id must uniquely identify a record in the STRUCT_SITE list. Note that this item need not be a number; it can be any unique identifier.