 Many ligand transport proteins bind particular small biomolecules and transport them to other locations in the body of a multicellular organism . These proteins must have a high binding affinity when their ligand is present in high concentrations , but must also release the ligand when it is present at low concentrations in the target tissues . The canonical example of a ligand @-@ binding protein is <unk> , which transports oxygen from the lungs to other organs and tissues in all vertebrates and has close <unk> in every biological kingdom . <unk> are sugar @-@ binding proteins which are highly specific for their sugar <unk> . <unk> typically play a role in biological recognition phenomena involving cells and proteins . <unk> and hormones are highly specific binding proteins . 
