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Biomedical subjects

S M Ting

Publications and source records attributed to S M Ting.

At least 19 recordsLinked to original sources
PubMed1994

Post-transcriptional regulation of glutamyl-prolyl-tRNA synthetase in rat salivary gland.

Treatment of rats with isoproterenol resulted in elevated levels of prolyl- and glutamyl-tRNA synthetase activities in the parotid and submandibular glands. This increase in enzyme activity was accompanied by an increase in the bi-functional glutamyl-prolyl-tRNA synthetase and of a low molecular weight form of prolyl-tRNA synthetase. Isoproterenol also induced the synthesis of proline-rich glycoproteins in the parotid and submandibular glands. Withdrawal from the drug was accompanied by a decline in prolyl- and glutamyl-tRNA synthetase activities and by a decline in the levels of proline-rich glycoproteins in the salivary gland. During the time course of isoproterenol treatment, little change in the levels of mRNA encoding the bi-functional glutamyl-prolyl-tRNA synthetase was detected by Northern blot analysis. These results indicate that the synthesis of glutamyl-prolyl-tRNA synthetase is regulated at a post-transcriptional step and that the synthesis of this bifunctional protein may be linked to the utilization of proline and glutamic acid in protein synthesis.

Amino Acyl-tRNA Synthetases↗
PubMed1992

Isolation of prolyl-tRNA synthetase as a free form and as a form associated with glutamyl-tRNA synthetase.

Rat liver prolyl-tRNA synthetase was purified as a dimer of M(r) 60,000 subunits not associated with other aminoacyl-tRNA synthetases and as a form associated with glutamyl-tRNA synthetase. Proteolysis of the dimeric enzyme generated a less active form with M(r) 52,000 subunits and an inactive form with M(r) 40,000 subunits. A second species was isolated with polypeptides of M(r) 60,000 and 150,000. This form dissociated during gel filtration chromatography being partially resolved into the M(r) 150,000 and 60,000 components; glutamyl-tRNA synthetase was associated with the larger polypeptide and prolyl-tRNA synthetase with the smaller component. Antibodies against the M(r) 60,000 polypeptide reacted with the M(r) 60,000 and 150,000 polypeptides. Gel filtration of extracts revealed multiple forms of prolyl- and glutamyl-tRNA synthetase. Antibody against the M(r) 60,000 component detected the M(r) 60,000 and 150,000 polypeptides throughout the chromatogram; these forms could be partially separated by polyethylene glycol fractionation. The M(r) 150,000 and 60,000 polypeptides were detected by Western blot analysis of crude extracts prepared under several conditions. Antibody to prolyl-tRNA synthetase reacted with a M(r) 150,000 polypeptide of the aminoacyl-tRNA synthetase core complex identified previously as glutamyl-tRNA synthetase.

Amino Acids↗
PubMed1992

Stereoselective binding and activity of oxotremorine analogs at muscarinic receptors in rat brain.

The activities of the enantiomers of BM-5 were examined to measure muscarinic cholinergic selectivity in the central nervous system. Autoradiographic studies assessed the ability of each enantiomer to inhibit the binding of [3H]-(R)-quinuclidinyl benzilate ([3H]-(R)-QNB) to muscarinic receptors in the rat brain. (+)-(R)-BM-5 inhibited [3H]-(R)-QNB binding to rat brain sections at concentrations below 1.0 microM, while 100-fold higher concentrations of (-)-(S)-BM-5 were required for comparable levels of inhibition. Analysis of the autoradiograms indicated that both stereoisomers had a similar distribution of high affinity binding sites. Each enantiomer displayed higher affinity for muscarinic receptors in the superior colliculi and lower affinity for receptors in the cerebral cortex and hippocampus. (+)-(R)-BM-5 and oxotremorine inhibited adenylyl cyclase activity in the cerebral cortex with efficacies comparable to that for acetylcholine. (+)-(R)-BM-5 was 26-fold more potent than (-)-(S)-BM-5 in inhibiting adenylyl cyclase. Oxotremorine-M and carbamylcholine stimulated phosphoinositide turnover in the cerebral cortex. Oxotremorine had lower activity and (+)-(R)-BM-5 was essentially inactive at comparable concentrations. The difference in activity of the two enantiomers indicates a remarkable stereochemical selectivity for muscarinic receptors. The stereoselectivity index is comparable for both the autoradiographic assays (48) and measures of adenylyl cyclase activity (26) in the cerebral cortex.

Adenylyl Cyclases↗
PubMed1991

Once weekly versus twice weekly subcutaneous administration of recombinant human erythropoietin in patients on continuous ambulatory peritoneal dialysis.

Twice weekly subcutaneous (s.c.) administration of recombinant human erythropoietin (rHuEPO) is effective in reversing renal anemia in CAPD patients. However the optimal frequency of administration has not been established. It would be more convenient to give rHuEPO by once weekly rather than twice weekly injection. We have therefore compared the effect of twice weekly versus once weekly s.c. administration of rHuEPO. Two groups of 10 CAPD patients were given the same starting dose of s.c. rHuEPO (100 U/kg body wt/week) either as a single weekly dose or twice weekly in divided doses. The rHuEPO dosage was then adjusted according to the hematologic response. The aim was to increase hemoglobin levels by about 1 g/dl per month. The target hemoglobin was 10 g/dl. After 16 weeks of treatment with rHuEPO, the hemoglobin levels rose from 6.6 +/- 1.2 (mean +/- SD) to 10.1 +/- 1.1 g/dl in the once weekly group and from 6.4 +/- 0.8 to 10.2 +/- 1.1 g/dl in the twice weekly group. The average doses of rHuEPO used during the study were 84 +/- 16 and 88 +/- 15 U/kg body wt/wk for the once weekly and twice weekly groups respectively. Subcutaneous administration of low dose rHuEPO is effective in reversing renal anemia. Similar responses were obtained with once weekly and twice weekly regimens. It is therefore acceptable and convenient for patients to receive one weekly s.c. injection of rHuEPO for the treatment of renal anemia.

Adult↗
PubMed1990

Characterization of a glucocorticoid-sensitive hippocampal protein.

Increased synthesis of a rat hippocampal protein with an apparent molecular weight (Mr) of 35,000 Da occurs in response to elevation of serum corticosterone levels. Subcellular fractionation has localized this protein in the cytosol. Two-dimensional gel electrophoresis indicated that this protein has an isoelectric point (IEP) of 6.6. A similar protein in liver has a slightly higher Mr and an IEP of 6.8. Increased synthesis of one additional hippocampal protein with an Mr of 46,000 Da and an IEP of 6.2 and of two other liver proteins, one with an Mr of 53,000 Da and an IEP of 6.2 and the other with an Mr of 45,000 Da and a range of IEPs from 8.7 to 7.8, was also seen after injection of corticosterone into rats. One possible identity of the 35,000 Da protein is glycerol 3-phosphate dehydrogenase (GPDH), based upon the reported Mr and IEP of this enzyme. The 35,000 Da hippocampal protein co-eluted from a gel filtration column with GPDH activity. No alteration of hippocampal GPDH activity was seen in intact rats 4 or 24 h after injection of either corticosterone or the type II receptor-specific agonist RU 28362. However, daily administration of corticosterone to rats beginning 10 days after adrenalectomy returned hippocampal GPDH activity to normal values after 2-3 days. In contrast, synthesis of the 35,000 Da protein was maximally increased 4 h after a single injection of steroid and not elevated at later times.

Adrenal Glands↗
PubMed1982

Response of adrenal 3beta-hydroxy-delta5-steroid dehydrogenase to adrenocorticotropin treatment in thiouracil-fed male mice.

A number of parallels can be drawn between the reported endocrine status of thiouracil-fed young rodents and that of aged animals, particularly with regard to the hypothalamus-pituitary-adrenal axis. Since the activity of the adrenal steroidogenic enzyme 3beta-hydroxy-delta5-steroid dehydrogenase (3beta-HSD) has been shown to be depressed in aged rats and mice, the present study was done to determine whether exposure of young mice to thiouracil had a similar effect on adrenal 3beta-HSD activity. Feeding the goitrogen thiouracil at 0.25% (w/w) of the maternal diet from conception, and keeping it 0.25% of the offsprings' diet after weaning, significantly elevated activity of 3beta-HSD per gram of adrenal gland above control levels in 4-month-old mice, perhaps to compensate for depressed adrenal mass. Daily subcutaneous injections of physiological saline (0.9%) for 4 days was sufficient to increase 3beta-HSD activity per gram of adrenal tissue in euthyroid (P less than 0.05) but not in thiouracil-fed mice. Subcutaneous administration of ACTH (2 IU daily for 4 days) significantly increased adrenal 3beta-HSD activity to comparable levels in thiouracil-fed and euthyroid animals. Thus, thiouracil enhances the activity of 3beta-HSD per gram of adrenal tissue and does not prevent response of enzyme activity to exogenous ACTH.

3-Hydroxysteroid Dehydrogenases↗
PubMed1970

Tissue NAD levels and the response to irradiation of cytotoxic drugs.

It has been shown that when (32)P counting from a tumour is continuous peaks in the count rate can sometimes be induced by large doses of nicotinic acid, nicotinic acid, nicotinamide or 3-acetylpyridine, but not by 6-aminonicotinamide. These (32)P counting peaks have been associated with the time of maximal new synthesis of nicotinamide adenine dinucleotide (NAD). Sensitization to irradiation or some cytotoxic drugs has been found at the peak of this new NAD synthesis. The radioprotective agents cysteamine, 2-aminoethylisothiouronium bromide (AET) and serotonin have been found to cause a rapid fall in tissue NAD levels. The results have been briefly discussed.

Animals↗