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R Miquelis

Publications and source records attributed to R Miquelis.

26 records · Page 2Linked to original sources
PubMed1987

The N-acetylglucosamine-specific receptor of the thyroid. Binding characteristics, partial characterization, and potential role.

The binding characteristics of the GlcNAc binding protein present in thyroid membranes (Consiglio, E., Shifrin, S., Yavin, Z., Ambesi-Impiombato, F.S., Rall, J.E., Salvatore, G., and Kohn, L.D. (1981) J. Biol. Chem. 256, 10592-10599) were reinvestigated using neoglycoproteins as probes. Plasma membrane preparations from porcine thyroid specifically bound 125I-GlcNAc35-bovine serum albumin. Binding was dependent on the presence of calcium. Binding of ligand to receptor was minimal at neutral pH and maximal at pH 5.0. Equilibrium binding studies indicated positive cooperativity of binding and a site capacity of about 60 pmol/mg of protein. Competition studies were compatible with a specificity hierarchy of GlcNAc much greater than Gal; no recognition of mannose, fucose, or glucose moieties was noted. The receptor was detergent-solubilized from plasma membrane preparations and on the basis of the defined binding properties, purified by chromatography on a GlcNAc-Sepharose affinity column. The purified GlcNAc thyroid receptor has a subunit molecular size of about 45 kDa and appears to be an oligomer composed of three subunits. The receptor was identified as a component of thyrocytes by in situ cytochemical localization with fluorescent neoglycoproteins. In certain cases it was mainly present on, or near, the apical cell surface. It is suggested that this GlcNAc receptor functions in thyroglobulin metabolism, possibly involved in recycling of internalized thyroglobulin molecules back into the follicular lumen.

Acetylglucosamine↗
PubMed1981

The thyroid lysosomal system: dynamic state of the organelles in relation to iodine release.

Endocytosis and hydrolysis of thyroglobulin (Tg) by the thyroid lysosomal system were studied in vivo in normal rats. By double labelling experiments, with 125I (old label) and 131I (new label), it was found that the well known preferential utilisation of newly labelled iodine by the thyroid follicles did not take place during endocytosis: the specific radioactivity (SRA = 131I/125I) was the same for the soluble Tg, luminal in origin, and the particulate Tg, lysosomal in origin. By contrast, the SRA of the total iodine content of the lysosomes was 2-15 times lower than the SRA of the soluble Tg. When the total lysosomal fraction (LT) was fractionated by size into subpopulations, with L1 less than LII less than LIII (Miquelis et al. [14]), it was found, after kinetics experiments, that SRA(LI) greater than SRA(LII) greater than SRA(LIII) for their iodine content. As observed after ultracentrifugation analysis on a discontinuous Ficoll gradient, only a small portion of the lysosomes is responsible for the difference of the SRA between LI and LT. Moreover, the LI subpopulation, significantly enriched in organelles of 0.03-0.25 micron diameter (Simon et al. [25], exhibits a higher acid phosphatase activity/beta-galactosidase activity ration than LT. It is suggested that 1) endocytosis is not preferential for newly iodinated Tg, 2) the thyroid lysosomes hydrolyse preferentially recently iodinated Tg, 3) Tg enters the cell by micropinocytosis, 4) the micropinocytotic vesicles fuse rapidly with primary lysosomes, 5) progressive release of iodinated compounds occur during the maturation of secondary lysosomes which fuse amongst themselves.

Animals↗
PubMed1975

[Bimodal secretion of thyroid hormones].

In rats receiving 50 mug of iodine daily, the turnover curve of plasmatic hormones is bimodal. Simultaneously, a flux of direct secretion and a flux of delayed secretion participate in the hormonal secretion. The second flux is about twenty times greater than the first one. The delay of its turnover is probably due to the diffusion of the molecules of thyroglobulin into the colloid.

Animals↗
PubMed1975

Iodinated particles in the rat thyroid. II. Lysosomal characteristics.

In a previous study (Simon et al. 1971) a procedure for the preparation and separation of iodinated particles was described in the rat. The present paper deals with further investigations on the nature of these particles. Acid phosphatase and iodine are conjointly sedimentable and display a latency that is unmasked on dilution in a hypo-osmotic medium and under acidification to pH 5.0. These properties together with the sensitivity to Triton X-100 are best accounted for by assuming that iodinated particles of the thyroid gland are lysosomes. Part of the particulate iodine is soluble in n-butanol (BEI fraction). The existence of this BEI fraction demonstrates that hydrolysis of thyroglobulin occurs within the particles which thus exhibit an acid protease activity. Both the sedimentable iodine pool and acid phosphatase are increased under TSH stimulation and decreased after thyroxine treatment. In addition, the general activity of the iodinated particles is dependent on the daily iodine intake as shown by the variation of their iodine pool, acid phosphatase activity and BEI fraction with the iodine diet. It is concluded that iodinated particles of the thyroid gland are secondary lysosomes which participate in iodine secretion under TSH control. By in vitro treatment with destabilizing media or after in vivo treatment with thyroxine, iodinated particles exhibit a parallel loss of iodine and acid phosphatase. After a short-term TSH treatment in vivo, their iodine pool is more increased than their acid phosphatase activity. It is concluded that, at least in the normal rat thyroid, iodinated particles are essentially secondary lysosomes; true colloid droplets actually accumulate only after sufficient TSH stimulation.

Acid Phosphatase↗
PubMed1974

Fractionation of iodinated particles and mitochondria from thyroid by zonal centrifugation and a study of their heterogeneity.

1. The subcellular particles of horse and rat thyroids were fractionated in a B XIV zonal rotor on a non-linear gradient of Ficoll after labelling with radioactive iodine in vitro (horse) or in vivo (rat). In the horse, the resulting fractions were analysed for radioactive iodine, protein and enzymes representative of certain subcellular particles. In the rat, iodine turnover and thyrotrophin stimulation were studied. 2. The population of iodinated particles could be subdivided into three main classes, characterized by differences in beta-galactosidase and acid phosphatase content and position in the gradient. The presence of a fourth class of particles is suggested. 3. It is concluded that iodinated particles isolated from the thyroid are essentially secondary lysosomes. Their heterogeneity is established with respect to their position in the gradient, their content of acid hydrolases and their iodine turnover. 4. The iodine pools of these secondary lysosomes are increased by thyrotrophin without any change in their number. 5. Their functional significance is discussed. 6. The distribution of mitochondria as judged by succinate dehydrogenase was also studied. The succinate dehydrogenase was spread throughout the gradient with a maximum of activity (40%) in the upper layer of the gradient. Separation of mitochondria from lysosomes by this method was not successful.

Acid Phosphatase↗