| Abstract: | A fraction of readily elutable rat liver nuclear proteins (nuclear globulins), analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, contains two proteins which reflect the thyroid status of the animal. The larger (n-band) protein is abundant in normal rat nuclei but diminished in hypothyroidism by thyroidectomy or hypophysectomy and restored with T3 treatment. It is also diminished in starvation, during which time T3 treatment of concurrent hypothyroxinemia is ineffective in tis restoration. Refeeding restores the n-band protein in starved normal rats but not in starved thyroidectomized (Tx) rats. GH does not restore this protein in either Tx or hypophysectomized (Hx) rats. The dual requirements of euthyroidism and adequate nutrition imply that the n-band protein is thyroid hormone dependent but not thyroid hormone specific. The smaller of the two nuclear globulins, the t-band protein, is prominent in Tx or Hx rats and is not altered by additional hypometabolic factors (starvation) or by nonthyroid hormone related hypermetabolic stimuli (refeeding or GH treatment of Hx rats). It is reduced in normal or T3-treated Tx or Hx rats regardless of simultaneous hypometabolic states (starvation or nonthyroid hormone-related deficiencies of hypopituitarism) or hypermetabolic states (refeeding, liver regeneration, or hyperthyroidism). The t-band protein thus appears to be inversely thyroid hormone specific in its concentration. Electrophoretic and chromatographic analysis suggest that the n-band protein is a 125,000 mol wt subunit of a 290,000 mol wt holoprotein. The t-band protein is a 70,000 mol wt peptide which exists, in part, as a monomer but largely as a subunit of a protein complex with a mol wt greater than 100,000. |
