Definition of "apo"

apo

adjective
not comparable
1. (biochemistry, of a protein) In an inactive, unbound state
  Quotations
  In this scenario, unbound proteins are predominantly in the ligand-free ("apo") structure.
  2009 January 30, Robert B. Best, Gerhard Hummer, “BIOCHEMISTRY: Unfolding the Secrets of Calmodulin”, in Science‎
noun
plural apos
1. (biochemistry) Short for apolipoprotein.