J. Biol. Chem., Vol. 266, Issue 25, 16415-16419, Sep, 1991
Novel cold-sensitive cytosolic 3,5,3'-triiodo-L-thyronine-binding proteins in human red blood cell. Isolation and characterization
AN Fanjul and RN Farias
Departamento de Bioquimica de la Nutricion, Instituto Superior de Investigaciones Biologicas, Consejo de Investigaciones Cientificas y Tecnicas-Universidad Nacional de Tucuman, Argentina.
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.
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