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Biomedical subjects

D S Jones

Publications and source records attributed to D S Jones.

At least 109 records · Page 6Linked to original sources
PubMed1985

Characterization of adrenocorticotropin receptors that appear when 3T3-L1 cells differentiate into adipocytes.

The binding of an 125I-labeled analog of ACTH, [125I]Tyr23,Phe2,Nle4-ACTH-(1-38), to differentiated 3T3-L1 fat cells was characterized. Time-dependent binding, which was inhibited by saturating concentrations of unlabeled ACTH (0.44 microM), could be demonstrated in the differentiated cells. Using 0.4 nM [125I]ACTH analog and increasing concentrations of ACTH, the half-maximal concentration for inhibition by ACTH was 4.3 nM. Scatchard analysis demonstrated a single class of ACTH binding. There were approximately 3500 binding sites/cell. The binding of [125I]ACTH analog was specific in that it could be displaced by ACTH, ACTH-(1-19), ACTH-(1-17), and N-acetyl-Ser1-ACTH, but not by high concentrations of insulin, beta-endorphin, or polylysine. There was an excellent correlation between the ability of ACTH and its analogs to inhibit [125I]ACTH analog binding and the ability of ACTH and its analogs to stimulate cAMP production. In contrast, no saturable binding could be demonstrated when undifferentiated 3T3-L1 fibroblasts, which are not responsive to ACTH, were studied. Thus, differentiation of 3T3-L1 cells into the adipocyte form is accompanied by the appearance of receptors for ACTH. These receptors allow the adipocytes to respond to ACTH.

Adipose Tissue↗
PubMed1985

Autoantibodies against the insulin receptor. Dissociation of the acute effects of the antibodies from the desensitization seen with prolonged exposure.

The effect of antibodies against the insulin receptor (anti-R) found in a patient with the type B syndrome of insulin resistance and acanthosis nigricans was characterized using 3T3-L1 cultured fat cells. Anti-R acutely mimicked the action of insulin by stimulating deoxyglucose uptake. With more prolonged exposure, this insulinomimetic effect decayed, glucose metabolism returned to basal levels, and the cells became severely resistant to the actions of insulin. As seen with anti-R from a previous patient, desensitization consisted of both a dramatic decrease in the maximal responsiveness of the cells to insulin and a shift in the dose-response curve for insulin-stimulated glucose oxidation. The acute and chronic effects of anti-R were then compared. The concentration of anti-R required to half-maximally inhibit insulin binding averaged more than twice that required for half-maximal stimulation of deoxyglucose uptake, consistent with the amount of spare receptors in 3T3-L1 cells. After prolonged exposure, the insulinomimetic activity was completely lost at all concentrations of anti-R, even at those that did not completely induce insulin resistance. Thus, loss of the insulinomimetic activity of anti-R is necessary, but not sufficient, to cause desensitization. Less anti-R was required to desensitize cells to insulin than would have been predicted on the basis of the acute inhibition of binding and the number of spare receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Insulin-stimulated methylaminoisobutyric acid uptake in 3T3-L1 fibroblasts and fat cells.

3T3-L1 fibroblasts and fat cells have been extensively used to study the development of insulin-stimulated glucose and lipid metabolism during adipocyte differentiation in vitro. In this paper we explore the ability of insulin to stimulate amino acid uptake in 3T3-L1 cells using the nonmetabolizable amino acid analog methylaminoisobutyric acid (MAIB). In differentiated 3T3-L1 fat cells, a 12-h preincubation with insulin was required for maximal stimulation of MAIB uptake. In contrast, in the undifferentiated fibroblasts, insulin stimulation peaked between 6 and 8 h and then declined significantly. Maximal stimulation of MAIB uptake in the differentiated fat cell exceeded that in the fibroblast phenotype. This increased ability of insulin to stimulate MAIB uptake in fat cells appeared within the first day after removal of the differentiation medium. 3T3-L1 fat cells were 30 times more sensitive to the effects of insulin on MAIB transport than the undifferentiated fibroblasts. These findings are consistent with previous data on insulin-stimulated deoxyglucose uptake, in that the increased sensitivity to insulin with differentiation is more than can be accounted for by the increase in receptor number. The activity of porcine proinsulin indicates that this stimulation reflects the known characteristics of the insulin receptor. The stimulation of MAIB uptake by insulin in 3T3-L1 fat cells was blocked by inhibitors of protein synthesis (cycloheximide and puromycin) and mRNA synthesis (actinomycin D). Colchicine, an inhibitor of microtubule function, showed little inhibition of insulin-stimulated MAIB uptake. Insulin stimulation of MAIB uptake was greater when 3T3-L1 cells were preincubated with insulin in the absence of essential amino acids. Basal transport in 3T3-L1 cells was not influenced by the presence or absence of amino acids. Thus, amino acid deprivation appears specifically to enhance the ability of insulin to stimulate amino acid transport in cultured adipocytes.

Adipose Tissue↗
PubMed1982

The nucleotide sequence of 5S rRNA from Scenedesmus obliquus.

The nucleotide sequence of the cytoplasmic 5S ribosomal RNA from Scenedesmusobliquus has been determined using post-labelling techniques. The sequence is closely related to the 5S RNA sequence of Chlorella and contains all the areas of invariant sequence which appear to be conserved in plant cytoplasmic 5S RNA species.

Base Sequence↗
PubMed1980

The nucleotide sequence of Scenedesmus obliquus chloroplast tRNAfMet.

The chloroplast initiator tRNAfMet from the green alga Scenedesmus obliquus has been purified and its sequence shown to be p C-G-C-A-G-G-A-U-A-G-A-G-C-A-G-U-C-U-Gm-G-D-A-G-C-U-C-m2(2)G-psi-G-G-G-G-C-U-C-A -U-A-A-psi-C-C-C-A-A-U-m7G-D-C-G-C-A-G-G-T-psi-C-A-A-A-U-C-C-U-G-C-U-C-C-U-G-C-A-A-C-C-A-OH. This structure is prokaryotic in character and displays close homologies with a blue green algal initiator tRNAfMet and bean chloroplast initiator tRNAfMet.

Anticodon↗
PubMed1980

Nucleotide sequence of Scenedesmus obliquus cytoplasmic initiator tRNA.

The cytoplasmic initiator tRNA from the green alga Scenedesmus obliquus has been purified and its sequence shown to be p A G C U G A G-U m G m G C G C A G D G G A A G C G psi m G A psi G G G C U C A U t A A--C C C A U A G m G D m C A C A G G A U C G m A A A C C U Gm U C U C A--G C U A C C A-O H. The sequence has been deduced and confirmed using several different P-post labelling techniques. The sequence is similar to those of other eukaryotic cytoplasmic initiator tRNAs and it has the sequence G A U C in place of the usual G T psi C. Although it resembles lower eukaryotic species in having a U preceding the anticodon and a modified G in the T psi C stem, in overall homology it is closer to the higher eukaryotic than to the fungal initiator tRNAs.

Base Sequence↗
PubMed1977

The aminoacylation of transfer ribonucleic acid. Recognition of methionine by Escherichia coli methionyl-transfer ribonucleic acid synthetase.

The mechanism of the recognition of methionine by Escherichia coli methionyl-tRNA synthetase was examined by a kinetic study of the recognition of methionine analogues in the ATP-PPi exchange reaction and the tRNA-aminoacylation reaction. The results show that the recognition mechanism consists of three parts: (1) the recognition of the size, shape and chemical nature of the amino acid side chain at the methionine-binding stage of the reaction; (2) the recognition of the length of the side chain at the stage of aminoacyl-adenylate complex-formation; (3) the recognition of the sulphur atom in the side chain at the stage of methionyl-tRNA formation. It is proposed that the sulphur atom interacts with the enzyme to induce a conformational change. A model of the active site incorporating the mechanism of methionine recognition is presented.

Adenosine Triphosphate↗
PubMed1977

Quantitative evidence for the helicoid relationship between the maxillary and mandibular occlusal surfaces.

A method for measuring the transverse inclination of molar teeth is described which enabled significant differences (P less than 0.001) between the three molars to be demonstrated for a sample of English Modern (n 24) and Romano-British (n20) skulls. No significant differences between the transverse molar inclinations were found for the Bronze Age (n 10) or the Neanderthal (n 8) sample.

Dental Occlusion↗
PubMed1976

The aminoacylation of transfer ribonucleic acid. Inhibitory effects of some amino acid analogues with altered side chains.

Several amino acid analogues that are able to replace amino acid residues in binding positions of the biologically active C-terminal tetrapeptide amide sequence, Trp-Met-Asp-PheNH2, of the gastrins were examined for their ability to inhibit the aminoacylation of tRNA in an Escherichia coli and rat liver system. Although in both systems the amino acid side chains are involved in the recognition process, the structural requirements of the side chain in the two systems are not comparable. Analogues of methionine and phenylalanine behaved similarly in the E. coli and rat liver systems, whereas analogues of tryptophan behaved differently. From the results it is possible to suggest structural features of the amino acid side chains which are required for recognition by the aminoacyl-tRNA synthetases.

Amino Acids↗