title: Novel cold-sensitive cytosolic 3,5,3'-triiodo-L-thyronine-binding proteins in human red blood cell. Isolation and characterization.
abstract: Four cytosolic 3,5,3'-triiodo-L-thyronine-binding proteins (CTBP) were isolated from hemoglobin-free human erythrocyte on DEAE-cellulose column by linear gradient of NaCl (0-0.4 M). CTBP I, II, and IV underwent rapid loss of their activities at low temperatures, whereas CTBP III was cold-insensitive. Reactivation of cold-inactivated CTBPs by warming was obtained at 20 and 37 degrees C. CTBP I, II, and IV were not inhibited by thiol-blocking agents, whereas CTBP III was blocked. Scatchard analysis of L-3,5,3'-triodo-thyronine binding showed a high affinity site with Kd on the order of 10(-10) M for CTBP II and Kd values of about 10(-9) M for CTBP I and IV and of about 10(-8) M for CTBP III. The order of affinity of iodothyronine analogues to CTBPs was similar in CTBP I, II, and IV but different in CTBP III. Chromatography on Sephacryl S-200 HR showed the elution of a single peak for each CTBP. The apparent molecular weights were about 200,000, 200,000, 25,000, and 60,000 for CTBP I, II, III, and IV, respectively. The physiological relevance of these CTBPs is discussed.
authors.affiliation: Departamento de Bioquimica de la Nutrición, Instituto Superior de Investigaciones Biológicas, Consejo de Investigaciones Cientificas y Técnicas-Universidad Nacional de Tucuman, Argentina.
authors.forename: A N
authors.initials: AN
authors.lastname: Fanjul
authors.forename: R N
authors.initials: RN
authors.lastname: Farias
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000302:isolation & purification* / Q000378:metabolism; D003600:Cytosol / Q000737:chemistry; D004912:Erythrocytes / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008565:Membrane Proteins / Q000302:isolation & purification* / Q000378:metabolism; D008970:Molecular Weight; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D013696:Temperature; D013963:Thyroid Hormones; D014284:Triiodothyronine / Q000378:metabolism*; D000097810:Thyroid Hormone-Binding Proteins
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D013438:Sulfhydryl Compounds; D013963:Thyroid Hormones; D014284:Triiodothyronine; D000097810:Thyroid Hormone-Binding Proteins