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C A Edwards

Publications and source records attributed to C A Edwards.

At least 109 records · Page 6Linked to original sources
PubMed1984

Site-specific phasing in the chromatin of the rDNA in Dictyostelium discoideum.

The rDNA in Dictyostelium discoideum is organized in linear, extrachromosomal, palindromic dimers of approximately 88 X 10(3) bases in length. The dimers are repeated about 90 times per haploid genome. Using indirect end-labeling, we have mapped micrococcal nuclease and DNAase I-sensitive sites in the chromatin near the rDNA telomeres. This region is 3' to the 36 S rRNA coding region and contains a single 5 S rRNA cistron but is primarily non-coding. We have observed somewhat irregularly spaced but specific phasing of nuclease-sensitive sites relative to the underlying DNA sequence. Comparison of the sites in chromatin with those in naked DNA reveals an unusual and striking pattern: the sites in naked DNA that are attacked most readily by both nucleases, presumably because of the specificity of the nucleases for certain sequences or physical characteristics of the DNA, appear to be the same sites that are most protected in chromatin. This pattern extends over most of a 10(4) base region, from the sequence immediately distal to the 36 S rRNA coding region and extending to the terminus. Although much of the sequence-specific phasing is irregularly spaced, salt extraction data are consistent with the presence of nucleosomes. In addition, phasing in the terminal region may be directed partially by proteins that do not bind DNA as tightly as do core histones. We present a model for phasing in spacer regions in which the sequence preferences of nucleases such as micrococcal nuclease and DNAase I may be useful tools in predicting nucleosome placement.

Base Sequence↗
PubMed1984

The effects of long term growth hormone releasing factor (GRF 1-40) administration on growth hormone secretion and synthesis in vitro.

The ability of human pancreatic GH releasing factor 1-40 (hpGRF 1-40) to release GH has been studied in rat anterior pituitary cells in primary culture. Over 24 hours hpGRF (1-40) increased total (cell content and secretion) production 2-fold with an ED50 of 20 pM. Subsequent hpGRF (1-40) stimulation of GH release was not affected by pretreatment when the fall in stored GH was taken into account. In contrast LH responses to gonadotrophin releasing hormone (GnRH) were markedly desensitized after 24 hours GnRH pretreatment in the same experimental system and using the same analysis. hpGRF (1-40) responses were not desensitized when pretreatment was for 3, 12 or 24 hours. The data show that hpGRF (1-40) responses do not desensitize in our experimental conditions under which GnRH responses show marked desensitization.

Animals↗
PubMed1984

Prolactin response to thyrotropin-releasing hormone stimulation and dopaminergic inhibition in benign breast disease.

Pituitary function was tested in predefined clinical groups of benign breast disease under strictly controlled clinical and laboratory conditions. Two different tests of prolactin storage and control mechanisms, direct stimulation by thyrotropin-releasing hormone (TRH) and inhibition of dopaminergic control by domperidone, indicate a significant abnormality in patients with severe cyclical mastalgia and nodular breast disease (P less than 0.05 and P less than 0.002), but not in those with noncyclical mastalgia. No abnormalities of thyroid function were found.

Adult↗
PubMed1984

Altered responses of prolactin, luteinizing hormone and follicle stimulating hormone secretion to thyrotrophin releasing hormone/gonadotrophin releasing hormone stimulation in cyclical mastalgia.

A generalized abnormality of hypothalamopituitary function was found in 17 patients with cyclical pronounced mastalgia compared with 11 controls by using a combined thyrotrophin releasing hormone and gonadotrophin releasing hormone test. The release of prolactin, luteinizing hormone and follicle stimulating hormone was significantly greater in cyclical mastalgia patients than in controls. Basal thyrotrophin, T3 and T4 levels were within the normal range in both groups indicating normal thyroid status in benign breast disease. The single measurement of oestrogen and progesterone in the luteal phase was not abnormal. These data demonstrate an alteration in lactotroph and gonadotroph function in patients with cyclical mastalgia. It is unknown at present whether this represents an appropriate cellular response to altered central or peripheral signals. There is no evidence to suggest, however, that the anterior pituitary cell types are abnormal per se.

Adult↗
PubMed1984

Relationship between postprandial motor activity in the human small intestine and the gastrointestinal transit of food.

Profiles for gastric emptying and colonic filling were determined in 20 normal volunteers by means of a gamma camera and dedicated minicomputer after ingestion of a radiolabeled solid meal. These were compared with intraluminal pressure activity, recorded simultaneously from three sites (each separated by 50 cm) in the small intestine by infusion manometry. Recordings were continued for at least 8 h or until all the radioactivity appeared in the colon. Colonic filling was approximately linear, occurring at an average rate of 16% of the meal residues per hour. There were significant inverse correlations (p less than 0.01) between the pressure activity in the proximal jejunum during the first 3 h after ingestion and the times taken for 50% and 80% of the meal residues to enter the colon, and direct correlations between total small intestinal pressure activity and the half-time for gastric emptying. Phase III of the interdigestive migrating motor complex appeared between 3 and 9 h after ingestion (when between 15% and 80% of the meal remained in the small intestine), but did not necessarily migrate to the next recording site until much later. The time of appearance of phase III in the proximal jejunum was directly correlated with the half-time for gastric emptying (p less than 0.05) and with the intraluminal pressure activity recorded at that site during the first 3 h after food ingestion (p less than 0.01). The time at which 80% of the meal residues had entered the colon was significantly shorter in 6 subjects, in whom a postprandial activity front appeared to migrate throughout the small bowel, compared with 13 subjects, in whom this did not occur (5.0 +/- 0.5 h vs. 7.0 +/- 0.4 h, p less than 0.01). These studies have shown that gastrointestinal transit of a solid meal is related to both fed and fasted intraluminal pressure activity in the small intestine.

Adult↗
PubMed1982

An analogue of ubiquinone which inhibits respiration by binding to the iron-sulfur protein of the cytochrome b-c1 segment of the mitochondrial respiratory chain.

A synthetic quinone, 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT), inhibits electron transfer reactions in the cytochrome b-c1 segment of the mitochondrial respiratory chain. Addition of UHDBT to isolated succinate-cytochrome c reductase complex has effects on reduction of the cytochromes b and c1 by succinate similar to those which result from removal of the iron-sulfur protein from the b-c1 complex. Thus, UHDBT inhibits reduction of cytochrome c1 by succinate and, if antimycin is added before succinate, UHDBT inhibits reduction of cytochrome b in addition to c1. UHDBT increases the midpoint potential of the iron-sulfur protein of the b-c1 complex from +280 to +350 mV at pH 7.2. The inhibitor also shifts the gx peak in the EPR spectrum of the iron-sulfur protein from g = 1.80 to 1.76 and shifts the gz peak from g = 2.02 to 2.03. It causes only a slight shift in the central gy = 1.90 signal. The efficacy of inhibition of cytochrome c reductase activity of isolated reductase complex by UHDBT appears to depend on the oxidation-reduction poise of some component(s) in the b-c1 complex. Inhibition is decreased and there is an extensive lag in the onset of inhibition under conditions favoring oxidation of the b-c1 complex; inhibition increases and the lag is eliminated under conditions favoring reduction of the b-c1 complex. The titer for inhibition of cytochrome c reductase activity of isolated reductase complex is one UHDBT per b-c1 complex. With reductase complex from which the iron-sulfur protein of the b-c1 complex is reversibly resolved, the titer for inhibition is proportional to the amount of iron-sulfur protein reconstituted to the complex. These results suggest that UHDBT inhibits mitochondrial respiration by binding to the iron-sulfur protein of the b-c1 complex, possibly at a site which is otherwise involved in binding ubiquinone, and that this binding is enhanced when the iron-sulfur protein is reduced.

Animals↗
PubMed1982

Function of the iron-sulfur protein of the cytochrome b-c1 segment in electron transfer reactions of the mitochondrial respiratory chain.

Resolution and reconstitution has been used to examine the involvement of the iron-sulfur protein of the cytochrome b-c1 segment in electron transfer reactions in this region of the mitochondrial respiratory chain. The iron-sulfur protein is required for electron transfer from succinate and from ubiquinol to cytochrome c1. It is not required for reduction of cytochrome b under these conditions, but it is required for oxidation of cytochrome b by cytochrome c plus cytochrome c oxidase. Removal of the iron-sulfur protein from the b-c1 complex prevents reduction of both cytochromes b and c1 by succinate or ubiquinol if antimycin is added to the depleted complex. As increasing amounts of iron-sulfur protein are reconstituted to the depleted complex, the amounts of cytochromes b and c1 reduced by succinate in the presence of antimycin increase and closely parallel the amounts of ubiquinol-cytochrome c reductase activity restored to the reconstituted complex, measured before addition of antimycin. The function of the iron-sulfur protein in these oxidation-reduction reactions is consistent with a cyclic pathway of electron transfer through the cytochrome b-c1 complex, in which the iron-sulfur protein functions as a ubiquinol-cytochrome c1/ubisemiquinone-cytochrome b oxidoreductase.

Animals↗
PubMed1982

A DNA-mediated transformation system for Dictyostelium discoideum.

We have established a transformation system for Dictyostelium discoideum. The transformation vector contains the protein coding region of the Tn5 neomycin resistance gene fused to the proposed promoter of the Dictyostelium actin 8 gene; the vector also contains a sequence that acts as an autonomously replicating sequence (ars) in yeast. Using this vector, we can transform Dictyostelium vegetative amoebae to be resistant to aminoglycoside G418 at a frequency of between 10(-6) and 10(-4) of the input cells. The transformed cell lines are stable and contain vector sequences integrated within chromosomal DNA.

Aminoglycosides↗
PubMed1981

Cytokinin-Active Ribonucleosides in Phaseolus RNA: I. IDENTIFICATION IN tRNA FROM ETIOLATED PHASEOLUS VULGARIS L. SEEDLINGS.

The cytokinin-active ribonucleosides present in tRNA from etiolated Phaseolus vulgaris L. seedlings have been isolated and identified as cis-ribosylzeatin, 2-methylthio-ribosylzeatin, and N(6)-(Delta(2)-isopentenyl)-adenosine. The structures of the compounds were established on the basis of their chromatographic properties and the mass spectra of their permethylated and perdeuteromethylated derivatives. Cis-ribosylzeatin was the major cytokinin-active constituent of tRNA from this source.

Journal Article↗
PubMed1981

Cytokinin-Active Ribonucleosides in Phaseolus RNA: II. DISTRIBUTION IN tRNA SPECIES FROM ETIOLATED P. VULGARIS L. SEEDLINGS.

The distribution of cytokinin-active ribonucleosides in tRNA species from etiolated Phaseolus vulgaris L. seedlings has been examined. Phaseolus tRNA was fractionated by benzoylated diethylaminoethyl-cellulose and RPC-5 chromatography, and the distribution of cytokinin activity was compared with the distribution of tRNA species expected to correspond to codons beginning with U. Phaseolus tRNA(Cys), tRNA(Trp), tRNA(Tyr), a major peak of tRNA(Phe), and a large fraction of tRNA(Leu) were devoid of cytokinin activity in the tobacco bioassay. Cytokinin activity was associated with all fractions containing tRNA(Ser) species and with minor tRNA(Leu) species. In addition, several anomalous peaks of cytokinin activity that could not be directly attributed to U group tRNA species were detected.

Journal Article↗
PubMed1980

Modified assay for determination of hydroxyproline in a tissue hydrolyzate.

A modified assay for the determination of hydroxyproline in tissue is presented. The modifications greatly reduce the time required for analysis of excised tissue as first introduced by Stegemann and Stalder [1]. These modifications include a change in the technique for tissue hydrolysis and a change in the preparation of the hydroxyproline oxidizing agent. The analysis utilizes the standard addition technique, eliminating the need for correction of matrix effects between the specimen and standard. This paper attempts to give a complete detailed description of the assay such that the procedure may be repeated without requiring additional reference material.

Animals↗
PubMed1980

Oddity learning in the pigeon as a function of the number of incorrect alternatives.

Pigeons' rate of learning a two-color oddity task increased as a function of the number of incorrect alternatives from 2 to 24 in Experiments 1, 2, and 3. In general, pigeons that were transferred from many-incorrect-alternative to two-incorrect-alternative oddity performed better than controls, but considerably below baseline (Experiments 2 and 3). In Experiment 4, pigeons showed no unconditioned tendency to peck the odd stimulus among 24 incorect alternatives, when pecks were nondifferentially reinforced, and in Experiment 5, when this procedure was preceded by oddity training, a progressive drop in odd-stimulus pecking was found. In Experiment 6, pigeons exposed to a nine-stimulus array in which the odd stimulus appeared (a) in the center or (b) separate from the array learned faster than when the odd stimulus was at the edge. This outcome suggests ththe figure-ground relation between the odd stimulus and the incorrect alternatives plays a role in the facilitation produced by increasing the number of incorrect alternatives but that poor performance on the standard, three-alternative oddity task appears to be due to center-odd trials which provide a difficult size or number discrimination.

Animals↗
PubMed1979

Purification of a reconstitutively active iron-sulfur protein (oxidation factor) from succinate . cytochrome c reductase complex of bovine heart mitochondria.

Oxidation factor, a protein required for electron transfer from succinate to cytochrome c in the mitochondrial respiratory chain, has been purified from isolated succinate . cytochrome c reductase complex. Purification of the protein has been followed by a reconstitution assay in which restoration of ubiquinol . cytochrome c reductase activity is proportional to the amount of oxidation factor added back to depleted reductase complex. The purified protein is a homogeneous polypeptide on acrylamide gel electrophoresis in sodium dodecyl sulfate and migrates with an apparent Mr = 24,500. Purified oxidation factor restores succinate . cytochrome c reductase and ubiquinol . cytochrome c reductase activities to depleted reductase complex. It is not required for succinate dehydrogenase nor for succinate . ubiquinone reductase activities of the reconstituted reductase complex. Oxidation factor co-electrophoreses with the iron-sulfur protein polypeptide of ubiquinol . cytochrome c reductase complex. The purified protein contains 56 nmol of nonheme iron and 36 nmol of acid-labile sulfide/mg of protein and possesses an EPR spectrum with the characteristic "g = 1.90" signal identical to that of the iron-sulfur protein of the cytochrome b . c1 complex. In addition, the optimal conditions for extraction of oxidation factor, including reduction with hydrosulfite and treatment of the b . c1 complex with antimycin, are identical to those which facilitate extraction of the iron-sulfur protein from the b . c1 complex. These results indicate that oxidation factor is a reconstitutively active form of the iron-sulfur protein of the cytochrome b . c1 complex first discovered by Rieske and co-workers (Rieske, J.S., Maclennan, D.H., and Coleman, R. (1964) Biochem. Biophys. Res. Commun. 15, 338-344) and thus demonstrate that this iron-sulfur protein is required for electron transfer from ubiquinol to cytochrome c in the mitochondrial respiratory chain.

Animals↗
PubMed1979

The roles of the simian virus 40 tumor antigens in transformation of Chinese hamster lung cells.

Simian virus 40 mutants and deletions between 0.54 and 0.59 map units direct the synthesis of defective 20K t antigens (Crawford et al., 1978). These deletion mutants transformed actively growing CHL cells nearly as efficently as did wild-type virus, in either the focus formation assay or the growth in soft agar assay. In contrast, when CHL cells were in a resting state during infection, the transformation frequency of the mutants relative to wild-type dropped approximately 50 fold. The presence of the phorbol ester, TPA, diminished this difference. CHL cell lines transformed by the deletion mutants and selected by the focus assay grew almost as efficiently in soft agar as lines transformed by wild-type SV40. Both produced tumors in nude mice. The function of the 20K t antigen is discussed.

Animals↗