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K Sterling

Publications and source records attributed to K Sterling.

At least 19 recordsLinked to original sources
PubMed1991

Thyroid hormone action: identification of the mitochondrial thyroid hormone receptor as adenine nucleotide translocase.

A preliminary report from our laboratory suggested that the thyroid hormone triiodothyronine (T3) is bound with an association constant (Ka) approximating 2 x 10(11) M-1 by adenine nucleotide translocase (AdNT) purified from beef heart mitochondria. We now report that [125I]T3 is capable of photoaffinity labeling not only purified AdNT but also the carrier in intact beef heart mitochondria. Photoaffinity labeling in intact mitochondria was appreciably greater than that observed with purified AdNT. The covalently labeled AdNT was identified by 2-dimensional electrophoresis with pI of 10 on electrofocusing and M(r) of 31,000 on SDS gel. Identification of the covalently labeled protein as authentic AdNT was substantiated by its interaction with a specific monoclonal antibody preparation.

Animals↗
PubMed1988

Thyroid hormone action: early calorigenic effect on dispersed rat liver cells in the absence of protein synthesis.

Isolated dispersed rat liver cells were prepared by hypothyroid Sprague-Dawley rats. The cells were incubated under 95% O2/5% CO2 in Krebs-Ringer-bicarbonate buffer at pH 7.3-7.4 at 37 degrees C. The medium had been enriched with 2% bovine serum albumin (previously stripped of thyroid hormone) and 5-10 mM alanine as substrate. Two hour incubations were carried out with or without added triiodothyronine (T3) at 3 nM or 300-1,000 nM concentrations. Oxygen consumption determined at the end of the period of incubation with the Clark oxygen electrode showed stimulation above control values in the hormone treated flasks; parallel studies in which cycloheximide (100 microM) had been added to cells to block protein synthesis also showed enhanced oxygen consumption in response to T3. The results indicated a response to the hormone not dependent on new protein formation.

Animals↗
PubMed1987

Tissue-specific gene expression results from a purine- and pyrimidine-free diet and 6-mercaptopurine in the rat small intestine and colon.

Dietary purines and pyrimidines are not considered to have a nutritional role, much less a direct effect on the functioning of the gastrointestinal tract. We found that a dramatic decrease in adult rat small intestinal and colonic total ribonucleic acid (RNA) results from the removal of dietary purines and pyrimidines or the administration of 6-mercaptopurine. Ribonucleic acid hybridization analysis indicated specific decrease of the messenger ribonucleic acid (mRNA) for the purine salvage enzymes hypoxanthine-guanine phosphoribosyl transferase and adenine phosphoribosyl transferase in the small intestine and proximal colon but not in the liver of animals fed a diet lacking purines and pyrimidines. Levels of intestinal and hepatic beta-actin mRNA transcripts were generally not depressed by either diet or by the administration of 6-mercaptopurine. Liver hypoxanthine-guanine phosphoribosyl transferase and adenine phosphoribosyl transferase mRNAs were unaffected by the change in diet but were lowered by the administration of 6-mercaptopurine. These data indicate that nutrition and 6-mercaptopurine affect both total RNA, and individual mRNA concentrations at specific sites in the gastrointestinal tract. These findings are of potentially great significance because the regulation of intestinal total RNA levels and purine salvage mRNAs by both 6-mercaptopurine and a purine- and pyrimidine-free diet suggests a potential mechanism by which dietary components differentially control specific proteins synthesized in the body. These findings may be related to the efficacy of 6-mercaptopurine as well as so-called elemental diets as therapeutic agents in chronic inflammatory bowel disease (i.e., Crohn's disease).

Adenine Phosphoribosyltransferase↗
PubMed1987

Direct thyroid hormone activation of mitochondria: identification of adenine nucleotide translocase (AdNT) as the hormone receptor.

Earlier we presented preliminary data suggesting that the thyroid hormone triiodothyronine (T3) is bound with an association constant (Ka) approximating 2 X 10(11) M-1 by the ADP/ATP carrier, adenine nucleotide translocase (AdNT) purified from beef heart mitochondria (Endocrinology 110: 292, 1986). We now report that [125I] T3 is capable of photoaffinity labeling not only purified AdNT but also the carrier in intact beef heart mitochondria. The identity of the covalently labeled AdNT was corroborated by two dimensional electrophoresis (O'Farrell) with pI approximately 10 on electrofocusing (first dimension) and Mr approximately 31,000 on SDS gel (second dimension). Further identification of the covalently labeled material as authentic AdNT was afforded by recognition by specific monoclonal antibodies. Moreover, we found that addition of excess nonradioactive T3 to intact mitochondria or to mitochondrial protein solution prior to photoaffinity labeling resulted in inhibition of formation of labeled AdNT, compatible with saturation of limited capacity binding sites rather than nonspecific labeling with the ligand [125I] T3. It was considered highly significant that labeling in intact mitochondria was at least an order of magnitude greater than that observed with purified AdNT. This finding is compatible with our concept of an important role of the lipid microenvironment in the intact mitochondrial membrane in T3 binding.

Animals↗
PubMed1986

Direct thyroid hormone activation of mitochondria: the role of adenine nucleotide translocase.

A presumptive mitochondrial T3 receptor previously reported from this and other laboratories appears capable of accounting for the activation of liver mitochondrial oxidative phosphorylation within 30 min after iv bolus injection of nanogram doses of T3 into hypothyroid rats. The inner mitochondrial membrane carrier adenine nucleotide translocase (AdNT) catalyzes the exchange between the extra- and intramitochondrial ADP and ATP, and has been shown by measurements of flux control coefficients to exert a significant measure of control over the rate of mitochondrial oxidative phosphorylation. The activity of this carrier had been reported to be depressed below normal in hypothyroid rats and restored to normal by hormone replacement. Preparations of AdNT from beef heart mitochondria were found to exhibit high affinity, low capacity binding of [125I]T3. The findings make the mitochondrial carrier AdNT a strong candidate for the initiating site for thyroid hormone stimulation in mammalian species.

Animals↗
PubMed1978

Mitochondrial thyroid hormone receptor: localization and physiological significance.

Binding studies of thyroid hormone to submitochondrial fractions from rat liver suggest that the component responsible for high-affinity, low-capacity (saturable) binding of hormones arises from the inner mitochondrial membrane. The partially purified component, approximately 150,000 daltons, appears to be half protein and half lipid, largely phospholipids, tentatively identified as lecithin, phosphatidyl ethanolamine, and cardiolipin. A similar hormone-binding macromolecule was found in mitochondria from rabbit kidney, from human liver and kidney, and from rat kidney, myocardium, skeletal muscle, intestinal mucosa, whole small intestine, adipose tissue, and lung. It was absent from mitochondria of adult rat brain, spleen, and testis, organs calorigenically unresponsive to thyroid hormones injected in vivo, but was present in mitochondria from brains of rats 12 days old and younger. The organ distribution of the hormone-binding protein and its presence in neonatal brain mitochondria supports the biological relevance of the mitochondrial component as a thyroid hormone receptor.

Animals↗
PubMed1978

Partial purification of thyroid hormone receptor from mitochondrial inner membrane: evidence for a physiologic role.

Recently we described a protein component, from the inner mitochondrial membrane, which binds thyroid hormone with high affinity, low capacity (saturable) characteristics. This partially purified rat liver mitochondrial membrane component appears to be a 150,000 daltons lipoprotein complex. Phospholipids, tentatively identified as lecithin, phosphatidyl ethanoamine, and cardiolipin, appear to constitute 50% of this complex. A similar hormone binding marcomolecule was also found in mitochondria from rabbit kidney, as well as human liver and kidney. In the rat this saturable thyroid hormone binding component was found in mitochondria from liver, kidney, myocardium, skeletal muscle, intestinal mucosa, whole small intestine, adipose tissue, and lung. It was absent from the mitochondria of adult brain, spleen and testis, organs known to be calorigenically unresponsive to thyroid hormones injected in vivo. In contrast, neonatal rat brains contain the protein with binding constants similar to those of neonatal or adult rat liver mitochondria, but in older rat brains (14 and 17 days) the saturable binding was no longer present, as in adult brain. These data provide strong support for the biological relevance of the mitochondrial component as a thyroid hormone receptor.

Animals↗
PubMed1977

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.

Animals↗
PubMed1975

Thyroid hormone binding by a component of mitochondrial membrane.

The thyroid hormone, triiodothyronine, has been shown to be bound by the intranuclear chromatin protein associated with active DNA, where it is believed to stimulate transcription. Evidence exists that the thyroid hormones have direct action not only on nuclei, but also on mitochondria. Threfore, specific proteins that bind thyroid hormones in the mitochondria should be demonstrable. Mitochondria were isolated from homogenized rat livers by sedimentation through 0.25 M sucrose solution, followed by washing four times to free them of microsomes. Strong binding of thyroid hormones was observed in mitochondrial fractions prepared from both the membranes and the matrix. After incubation in an ice bath with increasing amonts of triiodothyronine with added tracer [125I]triiodothyronine, the matrix infrequently contained specific saturable receptor sites, but usually exhibited strong "nonspecific" interaction...

Animals↗
PubMed1975

Serum triiodothyronine concentration in thyroid storm.

Serum triiodothyronine levels were elevated in 6 patients with thyroid storm (769 plus or minus 181 ng/100 ml) but the values observed were not significantly different from those found in uncomplicated thyrotoxicosis (752 plus or minus 282 ng/100 ml). This observation suggests that the pathogenesis of thyroid storm resides in mechanisms other than a simple increase in serum triiodothyronine concentration.

Adolescent↗