Biomedical subjects

J Robbins

Publications and source records attributed to J Robbins.

At least 361 records · Page 20Linked to original sources

PubMed1976

Preparation and characterization of myosin copy DNA.

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Animals↗

PubMed1976

Thyroxine-binding globulin biosynthesis in isolated monkey hepatocytes.

Thyroxine-binding globulin biosynthesis was demonstrated in hepatocytes isolated from normal adult Rhesus monkeys. Dispersed cells were obtained by in situ liver perfusion with collagenase, hyaluronidase and EDTA. Conditions for optimum cell survival and incorporation of radioactive leucine into newly synthesized proteins were defined. Protein synthesis, and specifically thyroxine-binding globulin synthesis, were shown to continue throughout the incubation period, while cell survival remained high (75% excluded trypan blue after 6h). Incubation medium, cytosol and a particulate fraction (extracted with digitonin) were analyzed for thyroxine-binding globulin. After extensive dialysis and purification by affinity chromatography, newly synthesized thyroxine-binding globulin was identified by specific double-antibody immunoprecipitation and by immunodiffusion and immunoelectrophoresis with autoradiography. Newly synthesized thyroxine-binding globulin was present after 4 h of incubation. After 6 h, the total synthesized had increased to 150% of the 4 h value, while the fraction present in the medium and increased to 300%, indicating probable thyroxine-binding globulin secretion

Animals↗

PubMed1976

Use of lithium as an adjunct to radioiodine therapy of thyroid carcinoma.

The effect of lithium on iodine kinetics after oral 131I-iodide was studied in an athyreotic patient with follicular thyroid carcinoma. Lithium decreased the disappearance rate of 131I from the whole body and from a tumor mass in the patient's thigh from control values of 0.126/day, respectively, while having only a minimal effect on the rate of 131I disappearance from blood. The increased tumor 131I retention would be expected to increase the therapeutic:toxic ratio of 131I. However, a subsequent therapeutic dose of 131I-iodide given with lithium was accompanied by an unanticipated increase in blood 131I and, therefore, in whole body radiation, resulting in significant bone marrow depression. Although lithium may be a useful adjunct in 131I therapy of functional thyroid carcinoma, it must be used cautiously in future studies.

Adult↗

PubMed1976

Radioimmunoassay for serum thyroxine-binding globulin: results in normal subjects and in patients with hepatocellular carcinoma.

Serum thyroxine-binding globulin (TBG) was measured by radioimmunoassay. The human TBG used in this study was purified by affinity, anion-exchange, and gel filtration chromatography. The serum TBG concentration in 98 euthyroid normals was 1.48 +/- 0.46 mg/100 ml (mean +/- SD), which is one-half that previously reported using a similar method. The level in females (1.66 +/- 0.56) was significantly higher than that in males (1.37 +/- 0.37). Comparison of the serum TBG level and the maximum binding capacity of serum TBG for thyroxine (T4) yielded a molar ratio of 1:1 for T4 and TBG. The mean serum TBG in 19 patients with hepatocellular carcinoma was 2.10 +/- 1.29 mg/100 ml; however, only 2 of these patients had serum TBG levels outside the normal range.

Adult↗

PubMed1976

Thyroxine-binding proteins.

As is the case for most small molecules in the body, the thyroid hormones are involved in interaction with proteins. The present discussion has centered on the hormone-protein interactions which occur in plasma. Although some of this is with proteins which also engage in other binding reactions, at least one protein, TBG, seems to exist only for the purpose of binding the thyroid hormones, and the interaction energy is extremely high. While this would lead us to suspect that is has an important role in hormone physiology, its function seems to be only of secondary significance. The peculiar role of PA in the transport of a vitamin as well as thyroid hormones also suggests a specific function, but none has become apparent. Knowledge of these proteins and their variation are of considerable importance to several commonly employed diagnostic tests of thyroid function. Their greatest importance at the present time, however, seems to be as models of thyroid hormone-protein interaction. The rapid advances being made in the isolation and characterization of TBG and PA provide the means to gain detailed chemical knowledge about two rather different types of binding sites. Hopefully, this will form the basis for similar knowledge about the active sites for the hormones on cellular proteins. Conceivably, this will help to further our understanding about the mechanism of hormone action.

Alpha-Globulins↗

PubMed1975

The site of sialic acid incorporation into thyroglobulin in the thyroid gland.

Iodine incorporation into thyroglobulin is known to occur within the lumen of the thyroid follicle. Since incorporation of sialic acid, which occupies a terminal position in the oligosaccharide chains, is also a later event in thyroglobulin synthesis, the possibility that sialic acid might be incorporated after thyroglobulin secretion was investigated. In one experimental approach normal rat thyroid hemilobes were incubated with radioactive precursors. Thyroglobulin, analyzed by equilibrium centrifugation in RbCl, had a median density which varied according to the moiety labeled in the following increasing order: leucine smaller than galactose smaller than sialic acid smaller than iodine. The molecules having the highest density were labeled only with iodine. In the second approach, thyroid hemilobes were taken from rats treated with cycloheximide for 16 hours to stop protein synthesis and allow nascent molecules to be secreted, and incorporation of precursors into thyroglobulin was analyzed by sucrose gradient centrifugation. Leucine incorporation was 6% of control but the amino acid was found in the NH2-terminal position. N-Acetylmannosamine (sialic acid precursor) and galactose incorporation were also completely inhibited whereas iodine incorporation was 10% of control. Incorporation was not restored by thyrotropin treatment, and the sialyltransferase and iodination systems were reduced only to 50 to 70% of control. The results indicate that sialic acid is incorporated only in nascent thyroglobulin and not in thyroglobulin molecules already secreted into the follicular lumen. A large fraction of the iodine incorporation also seems to occur in newly synthesized thyroglobulin.

Animals↗

PubMed1975

Negative cooperativity in the binding of thyroxine to human serum prealbumin. Preparation of tritium-labeled 8-anilino-1-naphthalenesulfonic acid.

The binding of thyroxine (T4) and 8-anilino-1-naphthalenesulfonic acid (ANS) to human serum prealbumin was measured by equilibrium dialysis at pH 7.4 in 0.05 M phosphate-0.10 M NaCl at 25 degrees. The data were analyzed for the binding constants based on equations for (1) two independent sites and (2) two identical sites with negative interaction. Evaluation by the independent site model gave the following association constants: for T4 binding, KT1 = 1.0 x 10-8 M-1, KT2 = 9.5 x 10-5 M-1; for ANS binding, KA1 = 9.5 x 10-5 M-1, KA2 = 2.1 x 10-5 M-1. The interactive model gave constants kT = 5.5 x 10-7 M-1 and kA = 5.5 x 10-5 M-1. Interaction factors, alpha, defined such that -RT in alpha is the energy of interaction, were: alpha T = 0.041 AND ALPHA A = 0.62 for T4 and ANS, respectively. The "best fit" values for the number of sites were 2.0 and 1.6 for T4 and ANS, respectively. The binding of T4 to human prealbumin was competitive with ANS, and the binding constants evaluated from competition experiments were in agreement with those found for each ligand when studied separately. On the basis of analysis of X-ray data of human prealbumin (Blake et al.) there appear to be two identical T4 sites. It is therefore evident that the binding of T4 represents a case of negative cooperativity which is presumably due to interaction between ligands.

Anilino Naphthalenesulfonates↗

PubMed1975

Defective thyroglobulin synthesis in an experimental rat thyroid tumor: iodination and thyroid hormone synthesis in isolated tumor thyroglobulin.

Purified rat tumor thyroglobulin from the experimental rat thyroid tumor, line 1-1C2, was studied for its thyroid hormone content after in vivo and in vitro iodination and compared with normal and desialylated normal rat thyroglobulin. Tumor thyroglobulin had a very low sialic acid and iodine content; after in vivo iodination it contained only small amounts of triiodothyronine (T3) and no detectable thyroxine (T4). After in vitro iodination with 125I it showed a distribution of T3 and T4 very similar to that of normal and desialylated normal thyroglobulin iodinated in vitro. In vitro iodination dissociated tumor and desialylated normal thyroglobulin to a greater extent than normal thyroglobulin. Tumor tissue, on the other hand, showed considerable iodinating activity in the 105,000 X g pellet when studied with exogenous acceptors. These results are compatible with a role for sialic acid in the maturation and migration of thyroglobulin to the iodination site, rpovided that the intracellular distribution of the iodinating enzymes are normal.

Animals↗

PubMed1974