Isolation and properties of a native subunit of lamprey thyroglobulin.

Abstract The thyroglobulin-like iodoproteins from lamprey thyroid tissue were prepared by repeated salting out between 1.4 and 1.8 m ammonium sulfate. Velocity ultracentrifugation showed only two boundaries, the sedimentation coefficients of which were about 5 S and 12 S. Sucrose gradient centrifugation of the same preparation, pulse-labeled with both 125I and 131I (7 days and 1 hour, respectively before killing), indicated the presence of a third component (17 S) which had a very rapid turnover and corresponds to native thyroglobulin of higher vertebrates. The 12 S component was obtained in ultracentrifugally homogeneous form with a sedimentation constant (s020,w) and molecular weight of 11.7 and 331,000, respectively. The iodine content was 0.003%. Lamprey 12 S thyroid protein, the first subunit of thyroglobulin which has been isolated in a pure form, is a native, stable protein with a molecular size corresponding to one-half that of the parent molecule, thyroglobulin