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D A Rice

Publications and source records attributed to D A Rice.

At least 19 recordsLinked to original sources
PubMed2001

Preparation and properties of gallaborane, GaBH(6): structure of the gaseous molecule H(2)Ga(mu-H)(2)BH(2) as determined by vibrational, electron diffraction, and ab initio studies, and structure of the crystalline solid at 110 K as determined by X-ray diffraction.

Gallaborane (GaBH(6), 1), synthesized by the metathesis of LiBH(4) with [H(2)GaCl](n) at ca. 250 K, has been characterized by chemical analysis and by its IR and (1)H and (11)B NMR spectra. The IR spectrum of the vapor at low pressure implies the presence of only one species, viz. H(2)Ga(mu-H)(2)BH(2), with a diborane-like structure conforming to C(2v) symmetry. The structure of this molecule has been determined by gas-phase electron diffraction (GED) measurements afforced by the results of ab initio molecular orbital calculations. Hence the principal distances (r(alpha) in A) and angles ( angle(alpha) in deg) are as follows: r(Ga.B), 2.197(3); r(Ga-H(t)), 1.555(6); r(Ga-H(b)), 1.800(6); r(B-H(t)), 1.189(7); r(B-H(b)), 1.286(7); angleH(b)-Ga-H(b), 71.6(4); and angleH(b)-B-H(b), 110.0(5) (t = terminal, b = bridging). Aggregation of the molecules occurs in the condensed phases. X-ray crystallographic studies of a single crystal at 110 K reveal a polymeric network with helical chains made up of alternating pseudotetrahedral GaH(4) and BH(4) units linked through single hydrogen bridges; the average Ga.B distance is now 2.473(7) A. The compound decomposes in the condensed phases at temperatures exceeding ca. 240 K with the formation of elemental Ga and H(2) and B(2)H(6). The reactions with NH(3), Me(3)N, and Me(3)P are also described.

Journal Article↗
PubMed2001

Postmortem biochemical markers of experimentally induced hypomagnesaemic tetany in cattle.

Severe hypomagnesaemia and tetany were induced in 10 lactating cows by feeding them semi-synthetic low magnesium diets and the animals were used to study the stability of postmortem markers of hypomagnesaemic tetany. There were significant relationships between the concentrations of magnesium in either cerebrospinal fluid (CSF) or plasma and either aqueous or vitreous humour. The onset of hypomagnesamic tetany was also associated with low magnesium concentrations in plasma, CSF and aqueous and vitreous humour. Magnesium concentrations less than 0.25 mmol/litre in fresh aqueous humour may be indicative of severe hypomagnesaemia and possible tetany in lactating cows, but the concentration of magnesium in aqueous humour was unstable postmortem. The concentration of magnesium in vitreous humour was relatively stable and a concentration of less than 0.55 mmol/litre could be used as a diagnostic marker of tetany in cattle for up to at least 48 hours postmortem, at ambient temperatures typical of Northern Ireland.

Animals↗
PubMed2000

Monochlorogallane: physical properties and structure of the gaseous molecule H2Ga(mu-Cl)2GaH2 as determined by vibrational, electron diffraction, and ab initio studies.

Monochlorogallane, synthesized by the metathesis of gallium(III) chloride with an excess of trimethylsilane at ca. 250 K, has been characterized by chemical analysis, by its IR, Raman, and 1H NMR spectra, and by the products of its reaction with trimethylamine. The vibrational spectra of the vapor species isolated in solid Ar, N2, or CH4 matrixes at ca. 12 K imply the presence of only one species, viz. the dimer with an equilibrium structure conforming to D2h symmetry. The structure of this molecule has been determined by gas-phase electron diffraction (GED) measurements augmented by the results of ab initio molecular orbital calculations. An equilibrium structure with D2h symmetry has been assumed in the analysis of the electron diffraction pattern. However, as the molecule has a very low frequency Ga(mu-Cl)2Ga ring-puckering mode, a dynamic model was used to describe it with the aid of a set of pseudoconformers spaced at even intervals (deltadelta = 5 degrees, deltamax, = 20 delta) around the ring-puckering angle delta and Boltzmann-weighted according to a quartic potential V(delta) = V4delta4 + V2delta2. The differences in bond distances and angles between the different pseudoconformers were constrained to the values derived from the ab initio calculations employing second-order Moller-Plesset (MP2) methods (with all the electrons included in the correlation calculations) and a 6-311G(d) basis set. The results for the weighted average of the principal distances (ralpha) and angles (<alpha) (with estimated 1sigma uncertainties) from the combined GED/ab initio study are r(Ga-Cl) 2.350(2) A, r(Ga-H) 1.523(20) A, <Cl-Ga-Cl 89.7(5)degrees, <H-Ga-H 135.1 degrees, V4 3.0 x 10(-6) kcal mol(-1) deg(-4), and V2 6.0 x 10(-4) kcal mol(-1) deg(-2).

Journal Article↗
PubMed2000

Expression of steroidogenic factor 1 in the testis requires an E box and CCAAT box in its promoter proximal region.

Steroidogenic factor 1 (SF-1), also known as adrenal 4-binding protein, is a member of the nuclear hormone receptor family that regulates transcription of genes encoding hormones and steroidogenic enzymes important to the function of the hypothalamic-pituitary-gonadal axis. The mammalian Ftz-F1 gene encodes SF-1 and is required for development of adrenal glands and gonads. To better understand the mechanisms regulating this gene in the gonads, we have examined its expression in the testis and characterized the promoter region for SF-1 in two testicular cell types. SF-1 promoter activity was examined in primary cultures of Sertoli cells and cell lines representative of Sertoli and Leydig cells. Deletion mutagenesis of the promoter identified several regions: both 5' and 3' to the transcriptional start sites that are important for transcriptional activity. Two elements, an E box and a CCAAT box, were found to be important for SF-1 transcription in the testis. An oligodeoxynucleotide containing both of these elements bound three specific protein complexes. The binding of one complex required only sequences within the E box and cross-reacted with antibodies against the basic helix-loop-helix ZIP proteins USF1 and USF2. A second specific complex required sequences within both the E box and CCAAT box for efficient binding, while a third complex predominantly interacted with sequences within the CCAAT motif. The presence of multiple protein complexes binding these sites suggests that regulation through these elements may involve interactions with different factors that depend on the state of the cell and its environment.

Animals↗
PubMed1996

Root surface removal with diamond-coated ultrasonic instruments: an in vitro and SEM study.

Adequate root preparation in periodontal procedures includes the removal of plaque, calculus, and perhaps contaminated cementum and dentin. The purpose of this study was to evaluate and compare the amount of root surface removal and residual surface texture using similarly shaped regular (US) and both fine (FINDIAM) and medium (MEDDIAM) grit diamond-coated ultrasonic inserts. Forty-five (45) premolars extracted for orthodontic reasons were randomly divided into 3 groups of 15 teeth each. They were individually mounted in a jig and instrumented with a standardized 500 gram force while they were moved a precise horizontal distance of 12 mm over a 1.2 second period using specially designed and computer controlled instrumentation. Three measurements were made to the nearest 0.0005" at 3 points along the test area before instrumentation and after 10 and 20 strokes. The mean depth of root structure removed was US 5.8 +/- 6.6 microns, FINDIAM 50.1 +/- 14.2 microns, MEDDIAM 30.8 +/- 12.1 microns, after 10 strokes, and US 12.7 +/- 10.9 microns, FINDIAM 83.3 +/- 20.1 microns, MEDDIAM 58.7 +/- 17.9 microns after 20 strokes, respectively. All 3 instruments were different from each other (P < 0.001) in the 10 stroke group, while in the 20 stroke group FINDIAM and MEDDIAM were different from US (P < 0.001), but not from each other. Only FINDIAM showed a significant difference between 10 and 20 stroke values for depth of root removal. Modified loss of tooth substance index SEM scores indicated increasingly greater root surface roughness from US to FINDIAM to MEDDIAM. Substantially greater root surface removal and greater residual root surface roughness occurred with diamond-coated ultrasonic inserts under standardized in vitro conditions. These results suggest that caution should be used with diamond-coated ultrasonic instruments during periodontal root planing procedures.

Analysis of Variance↗
PubMed1994

Pancreas disease in Atlantic salmon (Salmo salar) and vitamin E supplementation.

A study was instigated to investigate the histopathological and clinical pathological lesions associated with a naturally occurring pancreas disease (PD) outbreak in farmed Atlantic salmon. An attempt was made to reduce the severity of PD and associated lesions by altering the antioxidative and peroxidative substrates in the diets. The results do not support the hypothesis that PD leads to a vitamin E deficiency which induces a myopathy. PD was not associated with a reduction in tissue vitamin E concentrations. Despite high tissue vitamin E concentrations, pancreatic lesions and cardiac and skeletal myopathy occurred almost simultaneously. Severe myopathy appeared to be associated with high mortality. Dietary vitamin E concentrations > 500 mg/kg did not increase plasma and muscle vitamin E concentrations, which appear to be saturated. Liver concentrations were also high. However, differing concentrations of dietary vitamin E and fat were associated with differing mortality rates.

Animals↗
PubMed1992

Expression of a chimeric CaMV 35S Bacillus thuringiensis insecticidal protein gene in transgenic tobacco.

Insecticidal transgenic tobacco plants containing a truncated Bacillus thuringiensis cryIA(b) crystal protein (ICP) gene expressed from the CaMV 35S promoter were analyzed for ICP gene expression under field and greenhouse conditions over the course of a growing season. We present new information on temporal and tissue-specific expression of a CaMV 35S/cryIA(b) gene. Levels of cryIA(b) protein and mRNA were compared in both homozygous and hemizygous lines throughout plant development. Levels of ICP mRNA and protein increased during plant development with a pronounced rise in expression at the time of flowering. Homozygous ICP lines produced higher levels of ICP than the corresponding hemizygous lines. ELISA analysis of different tissues in the tobacco plant showed ICP gene expression in most tissues with a predominance of ICP in older tissue. All transgenic ICP tobacco lines which were studied in the field and greenhouse contained 400 ng to 1 microgram ICP per gram fresh weight in leaves from the mid-section of the plant at flowering. The amounts of ICP produced by field lines were directly comparable to levels observed in greenhouse-grown plants.

Bacillus thuringiensis↗
PubMed1992

Histopathologic and ultrastructural myocardial alterations in calves deficient in vitamin E and selenium and fed polyunsaturated fatty acids.

We developed an experimental model of nutritional degenerative myopathy in ruminant cattle. Fourteen experimental calves were fed a diet low in vitamin E and selenium for 127 to 137 days. Six of these calves were then euthanatized. After 127 days, a dietary additive of linseed oil that had been treated to protect it against ruminal hydrogenation was added to the low vitamin E and selenium diet of the eight remaining calves as a source of polyunsaturated fatty acids. Six of these animals were euthanatized after 6 to 11 days of polyunsaturated fatty acid feeding; the other two died after 6 and 8 days. Macroscopic myocardial alterations were seen in five polyunsaturated fatty acid-fed calves but not in any other experimental calf. Microscopic lesions, comprising multifocal or diffuse cardiocyte degeneration and necrosis, were seen in atrial and ventricular myocardium of all experimental calves. These changes were more severe in polyunsaturated fatty acid-fed calves than in animals that did not receive polyunsaturates. Ultrastructurally, sublethally damaged cardiocytes had lysed contractile material; vacuolated sarcoplasm; altered mitochondria, sarcoplasmic myelin figures, and lipofuscin granules; and multiple nuclei. Necrotic cardiocytes had contracted myofibrils, pyknotic nuclei, mineralized mitochondria, and plasmalemmal disruption; the external lamina remained largely intact. Necrosis was followed by macrophage invasion and phagocytosis of necrotic debris. Repair of the lesions was by deposition of collagen and elastin fibers. No alterations were seen in the hearts of control calves fed vitamin E and selenium-supplemented diet. The induced myocardial lesions are similar to those of spontaneous nutritional degenerative myopathy in ruminant cattle.

Animals↗
PubMed1992

Steroidogenic factor I, a key regulator of steroidogenic enzyme expression, is the mouse homolog of fushi tarazu-factor I.

We proposed that a cell-selective regulatory protein coordinately regulates the expression of three enzymes that are required for the biosynthesis of corticosteroids: cholesterol side chain cleavage enzyme, steroid 21-hydroxylase, and the aldosterone synthase isozyme of steroid 11 beta-hydroxylase. In this report, we identify a 53-kilodalton protein, termed steroidogenic factor 1 (SF-1), that interacts with the related promoter elements from these steroidogenic enzymes, and we isolate and characterize a cDNA that very likely encodes this protein. We first showed that nuclear extracts from bovine adrenal glands interact with the mouse steroidogenic regulatory elements, forming complexes indistinguishable from those produced by nuclear extracts from mouse Y1 adrenocortical cells. These bovine adrenal extracts were subjected to sequential ion exchange and affinity chromatography to yield a highly enriched preparation of SF-1. The predominant protein in the affinity-purified preparation comigrated with shift activity and had a mol wt of 53,000; UV cross-linking experiments demonstrated directly that this 53-kilodalton protein interacted with the steroidogenic regulatory element. Even with this marked enrichment, affinity-purified SF-1 bound six steroidogenic regulatory elements. These results support strongly the model that a steroidogenic cell-selective protein interacts with related promoter elements from three steroidogenic enzymes to regulate their coordinate expression. The recognition sequence of SF-1 closely resembles those of nuclear hormone receptor family members, suggesting that SF-1 may belong to this supergene family. By screening a Y1 cell cDNA library with the DNA-binding region of the H-2RIIBP nuclear hormone receptor cDNA, we isolated a cDNA that is selectively expressed in steroidogenic cells. When expressed as a glutathione S-transferase fusion protein in Escherichia. coli, the protein encoded by this cDNA interacts with all six related steroidogenic regulatory elements with a binding specificity indistinguishable from that of SF-1. Surprisingly, the sequence of the putative DNA-binding domain of this cDNA matches exactly the corresponding sequence of the mouse homolog of the Drosophila transcription factor fushi tarazu-factor I. The demonstration that a member of the nuclear hormone receptor family interacts with the steroidogenic regulatory elements provides intriguing insights into possible mechanisms by which these essential genes are regulated.

Adrenal Glands↗
PubMed1991

Sequential changes in propionate metabolism during the development of cobalt/vitamin B12 deficiency in sheep.

The changes in propionate metabolism that accompany cobalt deficiency in sheep are described. Two groups of sheep, fed either a cobalt sufficient or deficient diet, were given an iv propionate load at intervals during a 14 w experiment. There was a tendency towards increased propionate half-life as the animals became cobalt deficient. However, significant changes in the area under the plasma methylmalonic acid-time curve occurred very early, indicating significant impairment of propionate metabolism. Despite this, the area under the plasma glucose-time curve was unaffected by cobalt deficiency, suggesting that the impairment of propionate metabolism, although significant, is not extensive.

Animals↗
PubMed1991

A shared promoter element regulates the expression of three steroidogenic enzymes.

The adrenal cortex of the mouse coordinately expresses three cytochrome P450 enzymes that are required for the biosynthesis of corticosteroids: cholesterol side-chain cleavage enzyme (SCC), steroid 21-hydroxylase (21-OHase), and steroid 11 beta-hydroxylase (11 beta-OHase). Within their 5'-flanking regions, we previously identified six elements containing variations of an AGGTC motif that regulated expression in mouse Y1 adrenocortical cells: 21-OHase elements at -210, -140, and -65; SCC elements at -70 and -40; and an 11 beta-OHase element at -310. We demonstrate here that all six elements interact with the same, or closely related, DNA-binding protein(s). First, these elements all formed complexes of similar mobility in gel shift assays, suggesting that they interacted with protein(s) of similar size. Additional larger complexes were seen with those probes containing exact AGGTCA sequences. Second, competition experiments confirmed that the factor(s) interacting with different elements had closely related or identical recognition specificities. Finally, indistinguishable profiles of shift activities were seen upon fractionation of nuclear proteins over sequential chromatographic columns. Collectively, these results suggest that related elements interact with a shared protein to regulate three essential steroidogenic enzymes. An AGGTCA sequence motif comprises the response element for several members of the nuclear hormone receptor family. Oligonucleotide competitions and specific effects of antisera in gel shift assays implicated chicken ovalbumin upstream promoter-transcription factor in the formation of the larger complexes seen with the elements containing exact AGGTCA sequences. Therefore, this member of the nuclear hormone receptor family also may regulate the expression of the adrenal steroidogenic enzymes.

Adrenal Cortex Neoplasms↗
PubMed1990

Analysis of the promoter region of the gene encoding mouse cholesterol side-chain cleavage enzyme.

The cholesterol side-chain cleavage enzyme (SCC) catalyzes the initial and rate-limiting step in the synthesis of steroid hormones. The mouse gene encoding SCC was cloned and the nucleotide sequence of its 5'-flanking region determined. This sequence includes an AP-1 motif at -319 and two motifs, AGGTCA at -70 and AGCCTTG at -40, that match elements proposed to be important in the expression of steroid 21-hydroxylase. When transfected into mouse Y1 adrenocortical tumor cells, 1.5 kilobase pairs of 5'-flanking region of the SCC gene directed high levels of expression of a growth hormone reporter gene; treatment of the transfected Y1 cells with 8-bromo-cAMP increased this expression by 5-fold. In contrast, transfected mouse MA-10 Leydig cells showed appreciably lower expression, suggesting that SCC expression in Leydig cells requires additional elements not contained in the 5'-flanking region of the SCC gene used in these experiments. Deletion experiments showed that 424 base pairs of 5'-flanking sequences were sufficient for regulated expression in Y1 cells and mapped two regulatory regions: one from -424 to -327 and a second from -219 to -77. DNase I footprinting and gel mobility shift analyses of these 424 base pairs defined several interactions between nuclear proteins and the SCC promoter, including footprints centered over the AP-1 motif, over a sequence at -120, and over the sequences (-70 and -40) that resemble 21-hydroxylase promoter elements. Finally, site-selected mutagenesis of the potential elements at -40, -70, or -120 decreased SCC promoter activity in transfected Y1 adrenocortical cells, thus establishing their importance in SCC expression.

Adrenal Cortex Neoplasms↗
PubMed1990

Multiple regulatory elements determine adrenocortical expression of steroid 21-hydroxylase.

Steroid 21-hydroxylase (21-OHase) is specifically expressed at high levels in the adrenal cortex, where it is required for the synthesis of mineralocorticoids and glucocorticoids. In this study, we have investigated the regulatory elements in the 21-OHase promoter region which contribute to the expression of this gene in Y1 adrenocortical cells. Eight potential regulatory elements in the 5'-flanking region of the 21-OHase gene were identified by DNase I footprinting and gel mobility shift experiments. Some of these footprints were produced by nuclear extracts from many cell lines, whereas other interactions were seen only when using nuclear extracts from Y1 adrenocortical and MA-10 Leydig tumor cells. Mutation of most of the elements markedly decreased the expression of a 21-OHase gene transfected into Y1 cells, thus documenting their functional importance for expression. Moreover, oligonucleotides containing the sequences of two related elements at -65 and -210, which share the heptamer AGGTCAG, increased the activity of a heterologous promoter in a Y1 cell-specific manner. Collectively, these results demonstrate that expression of 21-OHase in Y1 adrenocortical cells requires interactions among multiple cis-acting elements and regulatory proteins.

Adrenal Cortex↗
PubMed1990

Structure-function studies of Na,K-ATPase. Site-directed mutagenesis of the border residues from the H1-H2 extracellular domain of the alpha subunit.

It has recently been shown that replacement of the border residues (Gln-111 and Asn-122) of the H1-H2 extracellular domain of the sheep Na,K-ATPase alpha subunit with the charged amino acids Arg and Asp generates a ouabain-resistant enzyme (Price, E. M. and Lingrel, J. B. (1988) Biochemistry 27, 8400-8408). In order to further study structure-function relationships in Na,K-ATPase, six additional mutations have been made at these border positions. Two of these mutants were single amino acid substitutions (Gln-111 to Arg or Asn-122 to Asp). These mutations change one or the other H1-H2 border residue to a charged amino acid. The remaining substitutions were double mutants in which both of the H1-H2 border residues were simultaneously changed to charged amino acids. Changes were made which introduced either positively charged amino acids (Lys at positions 111 and 122), negatively charged amino acids (Glu at positions 111 and 122) or oppositely charged amino acids (Lys at position 111 and Glu at 122; Asp at position 111 and Arg at 122) at the borders of the H1-H2 extracellular domain. HeLa cells transfected with any of these sheep Na,K-ATPase alpha subunit mutants were able to grow in concentrations of ouabain that were toxic to untransfected cells or cells transfected with the wild type sheep alpha subunit. Crude membranes isolated from the transfectants were analyzed for ouabain inhibitable Na,K-ATPase activity. All of the transfectants contained a relatively ouabain-resistant component of enzyme activity, with the ouabain I50 values ranging from 4 x 10(-3) M to 1 x 10(-6) M. The most resistant enzyme was the double mutant that contained Asp at position 111 and Arg at 122, whereas the least resistant were the enzymes containing the single amino acid substitutions. There was no correlation between the type of charged amino acid present at the border position and the degree of ouabain resistance. These data demonstrate the functional importance, in terms of ouabain binding, of the border positions of the H1-H2 extracellular domain of the Na,K-ATPase alpha subunit.

Animals↗