title: Properties of histidyl-proline diketopiperazine [cyclo(His-Pro)] binding sites in rat liver.
abstract: Characteristics of cyclo(His-Pro) binding sites in the rat liver were studied using 3H-labeled cyclo(His-Pro). Scatchard analysis suggested that the rat liver membrane had a single binding site with an apparent dissociation constant (Kd) of 7 X 10(-8) M. Pretreatment of membrane preparations with soybean trypsin inhibitor increased cyclo(His-Pro) binding, and the binding activity was sensitive to trypsin and phospholipase A digestion, suggesting that protein and phospholipid moieties are essential for cyclo(His-Pro) binding. Thiol reagents reduced binding activity, suggesting that the thiol group might be an important constituent of the cyclo(His-Pro) binding site. Cross-reactivities of TRH, TRH analogues, L-His and L-Pro were very low (0.2-9%). These findings indicate that specific binding sites for cyclo(His-Pro) in the rat liver have similar properties to the receptors for other polypeptides.
mesh_terms: D000818:Animals; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000378:metabolism*; D010741:Phospholipases A / Q000494:pharmacology; D010879:Piperazines / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000032:analysis* / Q000187:drug effects; D018025:Receptors, Thyrotropin-Releasing Hormone; D013347:Subcellular Fractions / Q000378:metabolism; D013379:Substrate Specificity; D014357:Trypsin / Q000494:pharmacology
chemical_list: D010456:Peptides, Cyclic; D010879:Piperazines; D011956:Receptors, Cell Surface; D018025:Receptors, Thyrotropin-Releasing Hormone; D010741:Phospholipases A; D014357:Trypsin; C015924:histidyl-proline diketopiperazine