Search PubMed⌕ Search

Biomedical subjects

S Lissitzky

Publications and source records attributed to S Lissitzky.

At least 55 records · Page 3Linked to original sources
PubMed1981

Effect of carboxypeptidase digestion of the human choriogonadotropin molecule on its thyrotropic activity.

Digestion of hCG by a mixture of carboxypeptidases B and Y results in an enzyme dose- and incubation time-dependent increase in its ability to stimulate the adenylate cyclase (AC) of human thyroid membranes. Treated under the same conditions [3 h at 37 C; enzyme to hCG ratio, 0.04 (wt/wt)], partially and highly purified hCG preparations display an increase of about 300% in thyroid AC-stimulating activity, while TSH displays a 30% decrease. In contrast, carboxypeptidase digestion of hCG under these conditions has no significant effect on its activity in the rat testis AC assay. The carboxypeptidase digestion results in cleavage of carboxyl-terminal amino acid residues 142--145 from the hCG beta-subunit; digestion of the hCG alpha-subunit is much less effective, as the carboxy-terminal amino acid residue 92 is removed from only about 13% of the hCG molecules. In accord with the results of amino acid analysis, a slight, if any, decrease in apparent molecular weight is found by gel filtration and polyacrylamide gel electrophoresis. In addition, carboxypeptidase digestion results in antigenic alterations of the molecule, as shown by a flatter slope of the dose-response curve in a hCG RIA and a 70% decrease in potency in a RIA that uses an antiserum to the hCG beta carboxy-terminal peptide. These data demonstrate that partial digestion of the hCG molecule with carboxypeptidase results in an increase in human thyroid AC-stimulating activity, with retention of the rat testis AC-stimulating activity.

Adenylyl Cyclases↗
PubMed1981

Follicle formation and iodide metabolism in cultures of human thyroid cells.

Primary cultures were initiated using thyroid tissue obtained at operation from patients with Graves's disease. The in-vitro conditions which permitted the formation of functional follicular structures in both primary cultures and derived sub-cultures were examined. In both situations, culture without the addition of calf serum to the medium resulted in the formation of follicles in response to thyrotrophin. In primary cultures the response to stimulation by exogenous thyrotrophin was variable. However, cells derived from long-term primary monolayers responded to thyrotrophin stimulation in a more predictable manner. In sub-cultures, the ability of cells to concentrate and organify iodide was augmented in a dose-dependent fashion in response to thyrotrophin (0 to 0.2 mu./ml); maximal values of 20 to 80 times those of control cultures being obtained. While follicular structure was maintained at higher hormone concentrations iodide-trapping capacity declined. Similar effects were produced by both low and high purity thyrotrophin and by dibutyryl cyclic AMP. Thyroid cells from two patients with a genetic defect of iodide organification exhibited the same lesion in vitro.

Cells, Cultured↗
PubMed1980

Binding of scorpion neurotoxins to chick embryonic heart cells in culture and relationship to calcium uptake and membrane potential.

Stimulation of 45Ca uptake by scorpion neurotoxins in cultured chick embryonic heart cells has been shown to be directly linked to their effect on sodium channels. This property was used to compare the activity of 15 neurotoxins from five different species to their lethal effect in the mouse and immunological properties. As scorpion neurotoxins, the alkaloid neurotoxin veratridine enhanced 45Ca uptake, and an apparent positive cooperativity between the two drugs was observed. 125I-Labeled toxin II from the scorpion Androctonus australis Hector was shown to bind to chick heart cells specifically, saturably, and reversibly with high affinity (KD = 1--3 nM in sodium-free medium) and low capacity (10--20 fmol/mg cell protein). As shown by 45Ca uptake and radioactive toxin binding experiments, the affinity of scorpion neurotoxin to heart cell receptors was dependent on external K+ concentration. Toxin binding was lowered by increasing Na+ concentration in the medium and was abolished by veratridine in a sodium (140 mM) containing medium. As previously reported for neuroblastoma cells, all these results are in agreement with the membrane potential dependence of scorpion neurotoxin affinity for its membrane receptor.

Animals↗
PubMed1980

An approach to the structure of thyroglobulin. Hormone-forming sequences in porcine thyroglobulin.

The mixture of CNBr peptides obtained by treatment of porcine thyroglobulin with cyanogen bromide was separated into three fractions by Sephadex G-200 gel filtration in 1 M propionic acid. When one of these fractions was reduced and S-alkylated, a hormone-containing CNBr peptide was purified by filtration on Biogel A-1.5 m and ion-exchange chromatography on DEAE-Sephadex. Similarly, two other hormone-containing CNBr peptides were separated from another reduced and S-alkylated fraction by Sephacryl S-200 gel filtration and DEAE-Sephadex chromatography. The three purified CNBr peptides have the same Mr (15000), differ in amino acid composition and contain 60-70% of the hormones present in the initial thyroglobulin. Fragmentation of these peptides into smaller hormone peptides was carried out by trypsin digestion followed by gel filtration. This resulted in the purification of eight discrete hormone-containing tryptic peptides whose homogeneity was established by the study of their N-terminal and C-terminal sequences. At least four sites for the synthesis of thyroxine and two sites for the synthesis of triiodothyronine have been identified in the three CNBr peptides. A possible additional site was recovered in the form of the peptides seryl-triiodothyronine and probably seryl-thyroxine. To gain information on the number of hormone-forming sites in thyroglobulin iodinated in vivo and on the distribution of these sites in the different hormone-containing peptides isolated, estimation of thyroxine and triiodothyronine content of batches of thyroglobulin of iodine content comprised between 0.73% and 1.6% was carried out, together with the estimation of the hormone content of all the CNBr peptides separated from two preparations of thyroglobulin of different iodine contents (0.73% and 1.23%). It was shown that the number of thyroxine and triiodothyronine residues increased linearly with increasing thyroglobulin iodine content in the range 0.73-1.6% and reached six residues of thyroxine and two residues of triiodothyronine/mol protein for a thyroglobulin iodine content of 1.6% with no indication of saturation. This result is at variance with previous findings on porcine thyroglobulin iodinated in vivo which suggested that the thyroxine content reached a plateau of three to four residues/molecule for an iodine content comprised between 0.7% and 1.1%.

Amino Acid Sequence↗
PubMed1979

Effect of gelatin on the cyclic AMP response of primocultured hog thyroid cells to acute thyrotropin stimulation.

The cyclic AMP response of cultured hog thyroid cells to acute thyrotropin stimulation was shown to be under a dual regulatory control by thyrotropin: both positive and negative regulation have been described. When added to the culture medium, gelatin (0.25%) promoted the reorganization of the cells into folicle-like structures, as does thyrotropin. Unlike thyrotropin, gelatin did not induce an increase in intracellular cyclic AMP but enhanced the acute cyclic AMP response to thyrotropin in cells cultured in gelatin-containing medium. When both gelatin and thyrotropin were present, the positive effect of low concentrations of hormone (less than 50 microU/ml) was increased whereas the refractory process observed in the presence of higher concentrations of hormone (greater than 50 microU/ml) was unchanged. These effects of gelatin might be mediated by interaction of the denatured collagen molecules with external proteins of the plasma membrane of thyroid cells.

Animals↗
PubMed1979

The interaction of radioiodinated thyrotropin with human plasma membranes from normal and diseased thyroid glands. Relation of thyrotropin binding to adenylate cyclase activity.

Plasma membranes have been purified from homogenates of normal human thyroid glands and multinodular euthyroid and Graves' goitres by discontinuous sucrose gradient centrifugation. Preparations of reasonable purity were obtained containing specific binding sites for thyrotropin and thyrotropin-sensitive adenylate cyclase. Optimum conditions for 125I-labeled thyrotropin binding were pH 7.8 and 37 degrees C. Sodium ions and concentration of Tris above 20 mM reduced thyrotropin binding. Human plasma membranes showed no species specificity toward thyrotropins from 3 different species (ox, hog and man). Displacement curves of I125-labeled bovine thyrotropin by unlabeled hormones was in the order of increasing concentrations of bovine, porcine and human highly purified thyrotropins and was inversely related to the specific biological activity of these preparations as determined by the bioassay in the mouse. Analysis of the interaction between membranes and 125I-labeled thyrotropin resulted in curvilinear Scatchard plots which can indicate the presence of two types of sites with high affinity -- low capacity (KD = 5 nM) and low affinity -- high capacity (KD = 500 nM) or site -- site interaction of the negative cooperativity type. No significant difference in binding site characteristics was found in normal and diseased glands (multinodular and Graves' goitres). A good correlation was found at equilibrium and in the conditions of adenylate cyclase assay between receptor occupancy and cyclase activation by b-thyrotropin.

Adenylyl Cyclases↗
PubMed1978

Modulation of adenylate cyclase/cyclic AMP response by thyrotropin and prostaglandin E2 in cultured thyroid cells. 1. Negative regulation.

Isolated porcine thyroid cells, cultured in the presence of thyrotropin (greater than or equal to 0.25 mU/ml) or prostaglandin E2 (greater than or equal to 0.1 micron), showed decreased adenosine 3':5'-monophosphate (cyclic AMP) response to further thyrotropin or prostaglandin E2 stimulation, respectively. Kinetics of the refractory process to thyrotropin and prostaglandin E2 are different: (a) maximal refractoriness to prostaglandin E2 was attained after 2--6 h exposure to prostaglandin E2 while refractoriness to thyrotropin was maximal only after 12--24 h; (b) the degree of refractoriness to prostaglandin E2 was much greater than that to thyrotropin. Refractoriness to thyrotropin or prostaglandin E2 is characterized: by specificity for each thyroid stimulator; by dependence upon the dose of thyrotropin or prostaglandin E2 in culture, e.g. induction of high degree of refractoriness with 0.5 mU/ml thyrotropin (or 1 micron prostaglandin E2), which elicits only a small cyclic AMP increase; by time requirement for induction; by partial effect; by changes of maximum activation of cyclic AMP response; by reversibility. This refractoriness of the cyclic AMP response was not induced by dibutyryl adenosine 3':5'-monophosphate. It was not attributed to increased cyclic AMP-phosphodiesterase activity, but to alterations in the receptor-adenylate cyclase system. Prevention of refractoriness to thyrotropin or prostaglandin E2 by incubation of cells in the presence of actinomycin D, puromycin and cycloheximide suggests that new RNA and protein syntheses are required for the development of the refractory state.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

Modulation of adenylate cyclase/cyclic AMP response by thyrotropin and prostaglandin E2 in cultured thyroid cells. 2. Positive regulation.

Two different independent processes are operating in cultured thyroid cells to regulate adenylate cyclase/cyclic AMP responsiveness to thyroid stimulators (thyrotropin and prostaglandin E2): firstly, refractoriness or negative regulation [preceding paper], which is specific for each thyroid stimulator, is not mediated by cyclic AMP and is not accompanied by alteration of adenylate cyclase activity; secondly, positive regulation which is characterized by an augmentation of the cyclic AMP response stimulated by thyrotropin and prostaglandin E2. This process is not specific for each thyroid stimulator and is a state of increased susceptibility of cyclic AMP synthesis to stimulation, accompanied by increased activity of the catalytic subunit of adenylate cyclase. Positive regulation is apparently mediated by increased intracellular cyclic AMP levels. It is a time-dependent and dose-dependent process. Very low concentrations (5-50 micronU/ml) of thyrotropin augmented cyclic AMP synthesis stimulated by thyrotropin and prostaglandin E2 whereas higher concentrations (above 0.1 mU/ml) augmented prostaglandin E2 stimulation but induced refractoriness to thyrotropin. Prostaglandin E2 (0.1 to 10 micronM) augmented thyrotropin stimulation and dibutyryl adenosine 3':5'-monophosphate (0.3 to 2 mM) augmented thyrotropin and prostaglandin E2 stimulation. Positive regulation is a slow process which develops within days and increases up to day 5 in culture. Experiments using inhibitors suggested that protein synthesis is required for the full expression of the increase in adenylate cyclase activity induced by the studied thyroid stimulators.

Adenylyl Cyclases↗
PubMed1978

Thyrotropin receptor-adenylate cyclase system in plasma membranes from normal and diseased human thyroid glands.

Thyrotropin binding characteristics and adenylate cyclase (AC) activity of thyroid plasma membranes were studied in 52 tissues from normal and diseased human thyroids. Data from normal glands, Graves' goiters, non toxic multinodular goiters and nodular and perinodular tissue of toxic nodular goiters show the same basal, TSH- and NaF- stimulated adenylate cyclase activities (no. = 45; 34.1 +/- 3.2 (m +/- SE), 378 +/- 43, 298 +/- 48 pmol cAMP x min-1 x mg membrane protein-1), the same stimulability of AC by TSH (11.3 +/- 1.4--fold over basal level) and by NaF (8.1 +/- 1.8-fold), the same apparent TSH binding equilibrium constants (5.6 +/- 0.7 and 406 +/- 57 nM) and the same TSH binding site concentrations (2.2 +/- 0.4, 27.8 +/- 5.9 pmol x mg membrane protein-1). Alterations of the TSH receptor and of the AC were detected in membranes from tumoral and metastatic lymph node tissues from thyroid papillary carcinoma and in the thyroid tissue from post-radioiodide therapy thyroiditis. These observations suggest that: (i) hyperthyroidism in Graves' disease or toxic nodular goiter does not result in and is not a consequence of an alteration in the TSH receptor-adenylate cyclase system; (ii) there is no evidence supporting a relationship between the studied membrane properties and clinical or histological status; (iii) membrane abnormalities detected in thyroid carcinoma vary widely; (iv) studies of these membrane alterations might be of interest in the therapeutic management of thyroid carcinoma and may lead to a better understanding of the receptor-adenylate system.

Adenylyl Cyclases↗
PubMed1978

[Interaction of TSH with human plasma membranes from normals and diseased thyroid glands (author's transl)].

Binding of TSH to plasma membranes purified from normal human thyroid gland is specific, saturable and dependent upon temperature, time, pH and salt concentration (standard assay conditions: 27 degrees C, 30 min, pH 7.8, 20 mM Tris). Displacement curve of 125I-TSH by unlabelled TSH shows a curvilinear relationship between B/F and B which can be interpreted by the presence of two sites with apparent binding constants about 5 nM and 500 nM and capacities of about 3 and 30 pmol/mg membrane protein, respectively. Systematic study of binding characteristics of membranes from 6 normal glands, 7 euthyroid multinodular goitres, 14 Graves' goitres and 2 toxic nodules do not show difference in the dissociation constants and capacities of sites between normal and diseased thyroid and between nodular and perinodular tissue in toxic nodules.

Cell Membrane↗