Jesus Nunez

Biosynthèse in vitro d'hormones marquées par 3H et 125I dans des coupes de corps thyroïde: I. Propriétés des coupes en survie

Abstract 1. 1. Sheep thyroid slices were incubated 24 h at 37° under appropriate conditions as described. They formed thyroid hormones labeled with 3 H and 125 I while histologically intact. 2. 2. The biological cycle of hormone formation was maintained in the gland slices studied in the presence of Na 125 I and of tritiated l -tyrosine. This was proven by several observations, among others the organification of 125 I, the incorporation of [ 3 H]tyrosine into thyroglobulin purified by Sephadex, and also the formation of labeled 3,5,3′-triiodothyronine and thyroxine.

Protéines iodées particulaires thyroïdiennes II. Biosynthèse protéique et iodation

Abstract 1. 1. Particles of sheep thyroid slices incubated in vitro with [ 3 H]tyrosine contain thyroglobulin (19 S) and lighter sub-units (12 S and 3–8 S). The proportion of the lighter compounds is higher after short incubation times. 2. 2. Double-labeling experiments with 125 I- and [ 3 H]tyrosine show that 3–8-, 12- and 19-S components are doubly labeled and that, during the incubation, the percentage of the former decreases while that of the others increases. 3. 3. The 3 H/ 125 I ratios for the different molecular species are established: the lighter the particulate iodoproteins and the longer the incubation time the more they are labeled by 3 H. 4. 4. The 3 H/ 125 I ratio of the 19-S protein from the soluble fraction is smaller than those of the particulate iodoproteins and the 19-S particulate compound. 5. 5. The identification of proteins which obviously belong to the same family, differing in their 125 I and 3 H content and morphological localization, confirms distinct sites for protein biosynthesis and iodination, there being two for the latter: colloidal and particulate. A scheme is proposed for coordination of the results obtained.

Biogénèse de la thyroglobuline: Les transitions d'halogénation

Abstract A model for the changes in properties of thyroglobulin during he course of its iodination has been established. 1. 1. The initial component of the heterogeneous molecular population which constitutes thyroglobulin is a non-iodinated protein (prethyroglobulin) which can be partially separated by chromatography on DEAE-Sephadex. Prethyroglobulin appears to be homogeneous. 2. 2. The stable thyroglobulin preformed in vivo and the preparation labeled by 125 I inv vitro atre heterogeneous, as shown by chromatography on DEAE-Sephzdex. The 2 populations contains molecules with the same iodine content. 3. 3. The iodine content of the total thyroglobulin corresponds to an average value. This protein must contain molecules with more than 60–70 atoms of iodine. 4. 4. The sedimentation coefficientd for the stable thyroglobulin (19 S) and for the preparation labeled in vivo (18.4 S) are average values. The heterogeneous populations contain molecules with lower (17 S) and higher (20 S from model iodination experiments) sedimentation coefficients. The iodination heterogeneity introduces conformational heterogeneity. 5. 5. Introduction of halogen (up to 60–70 iodine atoms) produces discrete transitions of conformation (shape or density changes) manifested in higher sedimetation velocity. A more striking transition occurs when an iodination level of 60–70 atoms is reached.

Synthèse acellulaire de la thyroglobuline et site d'iodation

Abstract Cell-free synthesis of thyroglobulin and the iodination site 1. 1. Thyroid microsomes and polysomes synthesize thyroglobulin (approx. 19 S) in cell-free systems. If it is a true protein synthesis, membranes appear therefore to be unnecessary. 2. 2. The 12-S precursor, observed in cellular systems, is absent in cell-free systems. Thyroglobulin is totally free in the medium. The ribonucleoprotein particles contain only the light labelled fraction apparently not related to thyroglobulin. The processes of chain liberation and polymerization are therefore different in cellular and cell-free systems. In the latter case it seems that the newly synthesized chains are freed by hybridization with the preformed thyroglobulin which is present in the cell sap. 3. 3. Thyroid microsomes iodinate thyroglobulin but also other proteins present in the medium. The specificity observed in cellular systems is lost in cell-free systems. Polysomes are devoid of iodinating activity. The iodination enzyme seems to be on the membranes. These results agree with the fact, previously established, that biosynthesis and iodination are accomplished on two different sites in cellular systems; a specific transport mechanism thus allows the thyroglobulin molecule to reach the iodination site.