Thyroid glands from 800 Sprague-Dawley rats have been excised from the animals and incubated in a culture medium for 30' in the presence of tracing amounts of a radioactive aminoacid (4,5 3H-leucine). The soluble thyroid extracts have been purified by repeated ammonium sulfate precipitations and several sucrose density gradient centrifugations. A protein component, whose sedimentation coefficient approximates to 6 S, has been isolated. Such a component coincides both by ultracentrifugation and electrophoresis with an 3H-6 S protein whose nature as a biosynthetic subunit of 19 S thyroglobulin has been well established. The 6 S stable protein isolated in the present study is slightly contaminated with serum albumin and immunoglobulins. It is concluded that very small quantities of a native stable subunit (6 S), probably in equilibrium with its polymer from (19 S), are present in soluble extracts from thyroid glands.
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Con il contributo del Ministero per i Beni e le Attività Culturali