Data items in the ENTITY_NAME_SYS category record the systematic
               name or names associated with the entity, and tell which system
               was is the source of the systematic name. In some cases, the
               entity name may not be the same as the name of the biological
               structure. For instance, hemoglobin alpha chain would be the
               entity common name, not hemoglobin.
 
     loop_
    _entity_name_sys.entity_id
    _entity_name_sys.name
      1   ECx.x.x.x
      2  'acetyl-Ile-Val-Asp-Sta-Ala-Ile-Sta'
      3  'H(2)0'