Characteristics of the Thyroid Iodide Translocator and of Iodide-Accumulating Phospholipid Vesicles^*

Abstract

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.

Examination of antithyroid effects of smoking products in cultured thyroid follicles: only thiocyanate is a potent antithyroid agent

“…The question can be raised how thiocyanate inhibits iodide transport. Saito et al have described thyroid iodide translocator, a Na-dependent iodide transport protein different from Na+K+ATPase, in the phospholipid vesi¬ cle of plasma membrane (26) and speculated that thiocyanate inhibits this system (9). Their model is also convenient to explain competitive inhibition of iodide transport as thiocyanate and iodide are common sub¬ strates for this iodide transporting protein (9).…”

Iodine, Thiocyanate and the Thyroid

“…Then the question arises how thiocyanate inhibits iodide transport. [19] have described thyroid iodide translocator, a Na dependent iodide transport protein different from Na + K + -ATPase, in the phospholipids vesicle of plasma membrane; and speculated that thiocyanate inhibits the system [17]. Their model is also convenient to explain competitive inhibition of iodide transport as thiocyanate and iodide are common substrates for the iodide transporting protein.…”

Biochemistry of the Elemental Halogens and Inorganic Halides

“…While a phospholipid was proposed in early work as the likely transporter, recent research, using a transport model consisting of phospholipid vesicles made from porcine thyroid plasma membranes, has suggested that a protein or a lipid-protein complex is involved. Thus, the translocator is heat sensitive, is sensitive to trypsin, and appears to be inserted in the lipid bilayer (Saito et al, 1984; reviewed by Wolff, 1983).…”