Characteristics of the thyroid iodide translocator and of iodide-accumulating phospholipid vesicles.
Some biochemical characteristics of the thyroid I- translocator and of I- accumulating phospholipid vesicles (P-vesicles) were studied. P-vesicles were made from thyroid plasma membranes (PM) and soybean phospholipids by sonication. The optimal incubation temperature for Na+-dependent I- accumulation in P-vesicles was from 18-26 C. Only a small amount of Na+-independent I- accumulation was observed at various incubation temperatures, but it increased in proportion with the temperature up to 36 C. The optimal incubation pH (7.0-7.5) was near the physiological extracellular pH. When PM were heated at 55 C for 30 min before preparation of P-vesicles, Na+-dependent I- accumulation in the vesicles decreased by 35%. When they were heated at 65 C for 30 min, the I- -accumulating activity was almost completely lost. The translocator was also inactivated when PM were sonicated at 37 C in the presence of trypsin. The internal and external administration of ouabain to the vesicles did not affect the activity of Na+-dependent I- accumulation. When PM were treated with sodium dodecyl sulfate at a final concentration of 0.2-0.6 mg/ml, the I- translocator was inactivated or detached from PM, whereas the ouabain-sensitive Na+, K+-ATPase activity was preserved in the PM fragments. These observations suggest that the thyroid I- translocator consists of a protein component that is bound to PM at a site separate from Na+,K+-ATPase.
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D007454:Iodides / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes; D008563:Membrane Lipids / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D013552:Swine; D013696:Temperature; D013961:Thyroid Gland / Q000378:metabolism*
D007454:Iodides; D008081:Liposomes; D008563:Membrane Lipids; D010743:Phospholipids; D012967:Sodium Dodecyl Sulfate; D000251:Adenosine Triphosphatases