Cytosol-binding protein of thyroxine and triiodothyronine in human and rat kidney tissue

Study of chemical species of iodine in human liver

The distribution and chemical species of iodine in various subcellular fractions of human liver were studied by using epithermal neutron activation analysis combined with chemical and biochemical separation techniques, such as gradient centrifugation and gel chromatography. It was found that the total iodine content orders in various subcellular fractions is as follows: nuclei > cytosol > mitochondria > lysosome > microsome. In the lysosomal fraction, iodine is mainly bound to macromolecules, whereas in the nuclei and mitochondrial fractions, mainly with lower-molecular-weight organic compounds. In the cytosol fraction, iodine is combined with three proteins, in which iodine is chiefly bound with mid- and high-molecular-weight proteins.

Lung development and the pulmonary surfactant system: hormonal ifluences

The effect of hormones on developmental events is not a new area of scientific investigation. However, in the last decade, the developing lung has been the focus of an increasing amount of basic and applied research. Inadequate development of the newborn's respiratory system precludes extra-uterine existence; indeed, such respiratory inadequacy has been a leading cause of death in premature infants. Tremendous strides have been made in understanding the basic cell biology of the developing lung. Much has been learned about the source, composition, and function of pulmonary surfactant, a surface-active material produced by the lung and essential to alveolar stability. Deficient stores of this material is a major etiologic factor in the respiratory distress syndrome of the newborn (RDS). This fact, coupled with observations that certain hormones can accelerate lung development and the consequent availability of adequate stores of pulmonary surfactant, has led to a large body of literaturae dealing with the effects of hormones (and other agents) on lung development. It is the purpose of this literature review (1) to discuss the various kinds of investigations which have linked surfactant synthesis to the type II pulmonary epithelial cell; and (2) to review the current status of research dealing with the effects of glucocorticoids and thyroid hormones on lung maturation.

Evidence for the rapid direct control both in vivo and in vitro of the efficiency of oxidative phosphorylation by 3,5,3'-tri-iodo-L-thyronine in rats

1. Examination of the distribution of L-tri-iodothyronine among rat liver tissue fractions after its intravenous injection into thyroidectomized rats focused attention on mitochondria at very short times after administration. By 15 min this fraction contained 18.5% of the tissue pool; however, the content had decreased sharply by 60 min and even further over the next 3 h. By contrast, the content in all other fractions was constant or increased over 4 h. About 60% of tissue hormone was bound to soluble protein. 2. Mitochondria isolated from thyroidectomized rats showed P/O ratios that were about 50% of those found in normal controls, with both succinate and pyruvate plus malate as substrates. There was no evidence of uncoupling; the respiratory-control ratio was about 6. 3. Mitochondria isolated 15 min after injection of tri-iodothyronine into thyroidectomized rats showed P/O ratios and respiratory-control ratios that were indistinguishable from those obtained in mitochondria from euthyroid animals. The oxidation rate was, however, not restored. 4. Incubation of homogenates of livers taken from thyroidectomized animals injected with L-tri-iodothyronine before isolation of the mitochondria restored the P/O ratio to normal; by contrast, direct addition of hormone to isolated mitochondria had no effect. The role of extramitochondrial factors in rapid tri-iodothyronine action is discussed. 5. Possible mechanisms by which tri-iodothyronine might rapidly alter phosphorylation efficiency are considered: it is concluded that control of adenine nucleotide translocase is unlikely to be involved. 6. The amounts of adenine nucleotides in liver were measured both after thyroidectomy and 15 min after intravenous tri-iodo-thyronine administration to thyroidectomized animals. The concentrations found are consistent with a decreased phosphorylation efficiency in thyroidectomized animals. Tri-iodothyronine injection resulted in very significant changes in the amounts of ATP, ADP and AMP, and in the [ATP]/[ADP] ratio, consonant with those expected from an increased efficiency of ADP phosphorylation. This suggests that the changes seen in isolated mitochondria may indeed reflect a rapid response of liver in vivo to tri-iodo-thyronine.

Thyroid hormone action: the mitochondrial pathway

The subcellular compartments have been investigated to compare proteins capable of binding triiodothyronine and thyroxine; specific binders have been found in cytosol, nuclei, and mitochondria from rat liver and kidney. The binding protein from the inner mitochondrial membrane had the highest association constant (greater than 10(11) liters per mole), suggesting possible direct hormone action on the mitochondria. Binding of hormone analogs was found to be related to known physiological potency, and stereospecific discrimination between L- and D-thyroxine was observed. The saturable receptor was found in the mitochondrial membranes of rat liver, kidney, myocardium, and skeletal muscle but not in mitochondria from the unresponsive tissues: brain, spleen, and testis. Oxidative phosphorylation by mitochondrial vesicles from hypothyroid rats increased after the addition of physiological concentrations of triiodothyronine, which corroborated direct hormone action on mitochondria.

Indole-acetic acid binding proteins in soybean cotyledon

Using the charcoal assay to separate free from bound hormone, the results showed that there is a high binding of IAA to cytosol proteins. Competition experiments were carried out using compounds with different auxin activity (indole-acetic acid, alphanaphtalene acetic acid, indole-butyric acid and phenyl-acetic acid), revealing that specificity of binding exists for those compounds with a molecular configuration appropiate for auxin activity. The protein nature of the indoleacetic acid-binding molecule was demonstrated by the use of enzymes and by its thermolability.

How specific are nuclear "receptors" for thyroid hormones?

The presence of "high-affinity-saturable" binding sites for thyroid hormones of similar characteristics not only in isolated nuclei but in all the major extranuclear cellular components, as well as the failure of cytosol to promote nuclear binding, invalidates the analogy with steroid hormone receptors and necessitates a more critical assessment of the physiological relevance of current approaches to binding of thyroid hormone in vitro nuclear preparations.