Data items in the ENTITY_KEYWORDS category specify keywords
               relevant to the molecular entities. Note that this list of
               keywords is separate from the list that is used for the
               STRUCT_BIOL data items and is intended to provide only the
               information that one would know about the molecular entity *if
               one did not know its structure*. Hence polypeptides are simply
               polypeptides, not cytokines or beta-alpha-barrels, and
               polyribonucleic acids are simply poly-RNA, not transfer-
               RNA.
 
    loop_
    _entity_keywords.entity_id
    _entity_keywords.text
      2  'natural product, inhibitor, reduced peptide'