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J Robbins

Publications and source records attributed to J Robbins.

At least 37 records · Page 2Linked to original sources
PubMed1977

Structure and stability of human thyroxine-binding globulin.

The secondary and tertiary structure of human plasma thyroxine-binding globulin (TBG) was investigated by circular dichroism and fluorescence properties. The relaxation time of TBG indicated that it is a compact, symmetric molecule. It was calculated from the far ultraviolet CD spectrum that about one-half of the peptide groups are equally distributed in alpha helical and beta structures. In the near ultraviolet, the CD spectrum of TBG was modified when thyroxine was bound. TBG was stable at temperatures below 50 degrees at pH 9 and below 35 degrees at pH 10.5. Below pH 5 tryptophanyl fluorescence revealed a molecular transition which followed first order kinetics. The transition resulted in an irreversible loss of binding of the hormone. Acidification to pH 3.4 produced only a minor change in the CD spectrum, in which some of the alpha helical peptides were converted to beta structure.

Circular Dichroism↗
PubMed1977

Affinity labeling of human serum prealbumin with N-bromoacetyl-L-thyroxine.

Affinity labeling of human serum prealbumin with N-bromoacetyl-L-thyroxine (BrAcT4) was used to investigate the binding domain for L-thyroxine (T4) on prealbumin. Fluorescence titration with 8-anilinonaphthalene-1-sulfonate revealed a strong and a weak binding site for BrAcT4 (K1 = 1 X 10(8) M-1; K2 = 1 X 10(6) M-1). The reaction of BrAcT4 with prealbumin to form a covalent bond was inhibited in the presence of T4 and binding of T4 to prealbumin was nearly abolished after affinity labeling with BrAcT4. Affinity labeling with 2 mol of BrAcT4/mol of prealbumin resulted in covalent binding of 1 mol of ligand. Acid hydrolysis of affinity-labeled prealbumin gave Nepsilon-carboxymethyllysine and iminodiacetic acid, the latter being derived from the NH2-terminal glycine. A combination of analytical procedures, including tryptic digestion after maleylation, cyanogen bromide cleavage, digestion with yeast protease C, and sequential Edman degradations, revealed that the Nepsilon-carboxymethyllysine was derived from lysine-9 and lysine-15 and that the affinity label had distributed itself among glycine-1, lysine-9, and lysine-15 in a ratio of 29:63:8.

Affinity Labels↗
PubMed1977

Effects of estrogen on thyroxine-binding globulin metabolism in rhesus monkeys.

To investigate the effects of estrogen on thyroxine-binding globulin (TBG) metabolism, 4 female Rhesus monkeys were studied before and 3-4 weeks after implantation of beta-estradiol (E2)-containing capsules. In addition, 2 of the animals were also studied for the first 7 days after the start of E2. Serum E2 increased 10-fold from 20 +/- 7 to 212 +/- 41 pg/ml. Serum TBG, initially 20.2 +/- 6 mug/ml, was elevated by 24 h after E2 implantation, and reached a steady level of 46.8 +/- 5.0 mug/ml by 7-10 days. For the turnover studies, highly purified [125I]iodo-TBG was injected iv and serum [125I]PBI and urinary 125I excretion were measured daily. TBG kinetics were evaluated by use of a compartmental model. Although a 2-compartment model was sufficient to fit the control and late E2 data, a 3-compartment model was developed in order to account for the modifications observed during the early E2 period. The final decay rate (k) of TBG was 0.26 +/- 0.01/day during the control period and was slightly lower after E2 (0.23 +/- 0.01/day). In the 2 monkeys studied during the early E2 period, the major effect of E2 was a stimulation of the TBG production rate. This was simulated in the model by a stepwise increase occurring in the last quarter of the first day after E2. There was also an abrupt redistribution of TBG in the compartments defined by the model. The total distribution or serum equivalent volume of TBG after 3-4 weeks of E2 increased 1.4-fold, from 338 +/- 37 ml to 458 +/- 22 ml, and the metabolic clearance rate increased 1.3-fold, from 90 +/- 10 ml/d to 113 +/- 12 ml/d. The increase in the final TBG production rate (2.9-fold) was only slightly greater than the rate calculated for the early E2 period, and was similar to the increase we have recently found in monkey hepatocytes studied in vitro after isolation from E2-treated animals. It appears that stimulation of hepatic synthesis of TBG accounts for the elevated serum levels of TBG observed after estrogen.

Animals↗
PubMed1977

Stimulation of thyroxine-binding globulin synthesis by isolated rhesus monkey hepatocytes after in vivo beta-estradiol administration.

The rate of in vitro production of thyroxine-binding globulin (TBG) was studied in hepatocytes isolated from 6 control rhesus monkeys (serum TBG: 19.6 +/- 0.5 micrograms/ml; mean +/- SE) and 6 monkeys treated for 4-5 weeks with beta-estradiol (E2) (serum TBG: 45.1 +/- 1.8 micrograms/ml). Incorporation of [3H]leucine into intracellular soluble and particle-bound TBG, and into secreted TBG was determined for incubation periods up to 9 h. TBG was purified by affinity chromatography and measured by specific immunoprecipitation. The absolute amount of [3H]TBG and the ratio of [3H]TBG to total labeled protein in the same fraction were 3-fold higher in the particulate fraction and in the incubation medium of hepatocytes isolated from E2-treated monkeys. In separate experiments, TBG accumulation in the medium was measured for periods up to 19 h by radioimmunoassay. A 2.4-fold increase was observed with hepatocytes from E2-treated monkeys (3.48 ng TBG/h/10(7) cells, compared to 1.46 in controls). Correction of the production rates for the number of cells surviving during the incubation, and assuming 10.2 x 10(9) cells per liver, gave TBG production rates of 250 micrograms/liver/day in hepatocytes from E2-treated monkeys and 104 micrograms/day in hepatocytes from control monkeys. These experiments demonstrate that estrogen increases in vitro synthesis and secretion of TBG by isolated hepatocytes. The observed 2.4 to 3-fold increase was similar to the 2.9-fold increase in TBG production measured in vivo by kinetic analysis of TBG metabolism.

Animals↗
PubMed1977

Characterization of abnormal thyroglobulin in a transplantable rat thyroid tumor.

The solube iodoproteins in a transplantable rat throid tumor (Wollman Line 1-8) were studied after in vivo labeling with 125 I and were partially purified by affinity chromatography on anti-thyroglobulin-AGAROSE. A major fraction ('Peak A') was excluded from gels of large pore size, but had a low sedimentation rate (approximately8S) and did not appear to contain aggregates. It had a high density (approximately1.4) which was possibly due to a high content of carbohydrate, since treatment with a crude glycosidase mixture lowered the density to approximately1.3. A second fraction ('Peak B') had a similar sedimentation coefficient (6-9S) but penetrated the same gels and had a lower density (approximately 1.3). Both proteins formed soluble complexes with antibodies against normal rat thyroglobulin, and had other properties somewhat similar to those of thyroglobulin. After hydrolysis, mono- and diiodotyrosine were the only iodoamino acids liberated. These iodoproteins appears to represent abnormal forms of thyroglobulin synthesized by the tumor.

Animals↗
PubMed1977

Fine-needle aspiration cytology in the preoperative diagnosis of thyroid nodules.

Fifty consecutive patients were studied to assess the utility of fine-needle aspiration cytology for the diagnosis of hypofunctioning thyroid nodules. In two patients, cysts were evacuated and did not recur. Thirty-three patients underwent excisional biopsy; the aspiration biopsy result was not a criterion for surgery. Satisfactory aspiration specimens were obtained in 32 patients (97%). The diagnosis in nine aspiration specimens was malignant; of these seven (78%) were correct and there was one false-positive and one occult carcinoma unrelated to the clinically detected nodule. Five aspirations showed suspected malignancy; of these, two were carcinoma, one was an occult carcinoma, and two were benign. Eighteen aspirations were interpreted as benign; of these, 17 (94%) were correct and the one false-negative diagnosis was a well-differentiated follicular carcinoma. The procedure is useful in assessing the need for surgery in high-risk patients and in selecting patients for thyroid-suppression therapy.

Adult↗
PubMed1976

Haematemesis.

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Child↗
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↗