Search PubMed⌕ Search

Biomedical subjects

R E Mitchell

Publications and source records attributed to R E Mitchell.

At least 37 records · Page 2Linked to original sources
PubMed1991

Conservation of Plasmid DNA Sequences in Coronatine-Producing Pathovars of Pseudomonas syringae.

In Pseudomonas syringae pv. tomato PT23.2, plasmid pPT23A (101 kb) is involved in synthesis of the phytotoxin coronatine (C. L. Bender, D. K. Malvick, and R. E. Mitchell, J. Bacteriol. 171:807-812, 1989). The physical characterization of mutations that abolished coronatine production indicated that at least 30 kb of pPT23A DNA are required for toxin synthesis. In the present study, P-labeled DNA fragments from the 30-kb region of pPT23A hybridized to plasmid DNAs from several coronatine-producing pathovars of P. syringae under conditions of high stringency. These experiments indicated that this region of pPT23A was strongly conserved in large plasmids (90 to 105 kb) that reside in P. syringae pv. atropurpurea, glycinea, and morsprunorum. The functional significance of the observed homology was demonstrated in marker-exchange experiments in which Tn5-inactivated sequences from the 30-kb region of pPT23A were used to mutate coronatine synthesis genes in the three heterologous pathovars. Physical characterization of the Tn5 insertions generated by marker exchange indicated that genes controlling coronatine synthesis in P. syringae pv. atropurpurea 1304, glycinea 4180, and morsprunorum 567 and 3714 were located on the large indigenous plasmids where homology was originally detected. Therefore, coronatine biosynthesis genes are strongly conserved in the plasmid DNAs of four producing pathovars, despite their disparate origins (California, Japan, New Zealand, Great Britain, and Italy).

Journal Article↗
PubMed1989

Plasmid-mediated production of the phytotoxin coronatine in Pseudomonas syringae pv. tomato.

Pseudomonas syringae pv. tomato PT23.2 produces the chlorosis-inducing phytotoxin coronatine. Thirty-eight chlorosis-defective mutants of PT23.2 were previously generated by using the transposon Tn5. Five mutants contained Tn5 insertions in the indigenous plasmid pPT23A; the remaining 33 mutants either were missing pPT23A (29 mutants) or contained deletions in this plasmid (4 mutants). These results suggested that pPT23A was involved in coronatine production in strain PT23.2. This plasmid was introduced into P. syringae pv. syringae PS61, which does not produce coronatine. A bioassay for coronatine suggested that PS61(pPT23A) transconjugants were able to make this phytotoxin. In a chemical analysis, organic acids were isolated from PT23.2, PS61, and the transconjugant PS61(pPT23A); these were derivatized to their methyl esters and analyzed by gas chromatography. The derivatized organic acids extracted from PT23.2 and PS61(pPT23A) contained peaks that corresponded to coronafacic acid, coronafacoylvaline, and coronatine, but these were absent in the extracts from the wild-type strain PS61. The identification of these components was confirmed by combined gas chromatography-mass spectrophotometry. Therefore, the acquisition of pPT23A by PS61 resulted in biosynthesis of coronafacic acid, coronafacoylvaline, and coronatine, clearly demonstrating the involvement of pPT23A in coronatine production in P. syringae pv. tomato.

Amino Acids↗
PubMed1986

Cardiovascular epidemiology, exercise, and health: 40-year followup of the U.S. Navy's "1000 aviators".

The interrelationship of aging, performance, and stress modification has been the subject of investigations in the U.S. Navy. Beginning in 1940, a study of 1,056 student and instructor pilots lowered previously high attrition rates in training by emphasizing both physical and psychological screening. After World War II, when 208 pilots in the group died, followup studies of the survivors were conducted in 1951, 1957, 1963, 1969-71, 1977, and 1980-81. In February 1981, 715 questionnaires were mailed to known survivors, with 500 replies subsequently analyzed. Additionally, 114 of the respondents who had previously been examined during 1969, were again examined in 1980-81; those individuals were markedly different in their lifestyle, particularly in exercising regularly, abstaining from cigarette smoking, and drinking alcoholic beverages moderately, as contrasted to 28 aviators also examined in 1969 who died in the interim. Healthy lifestyle may alter cardiovascular risk, preventing premature death.

Aerospace Medicine↗
PubMed1985

The inactivation of ornithine transcarbamoylase by N delta-(N'-sulpho-diaminophosphinyl)-L-ornithine.

Phaseolotoxin, a tripeptide inhibitor of ornithine transcarbamoylase, is a phytotoxin produced by Pseudomonas syringae pv. phaseolicola, the causal agent of halo-blight in beans. In vivo the toxin is cleaved to release N delta-(N'-sulpho-diaminophosphinyl)-L-ornithine, the major toxic chemical species present in diseased leaf tissue. This paper reports on the interaction between N delta-(N'-sulpho-diaminophosphinyl)-L-ornithine and ornithine transcarbamoylase. N delta-(N'-Sulpho-diaminophosphinyl)-L-ornithine was found to be a potent inactivator of the enzyme, in contrast with phaseolotoxin, which previously has been reported to inhibit the enzyme reversibly. Inactivation by N delta-(N'-[35S]sulpho-diaminophosphinyl)-L-ornithine resulted in the incorporation of 35S into ethanol-precipitated protein. The stoicheiometry of 35S incorporation was approximately 1 mol/mol of active sites. Inactivation was second-order and a rate constant of 10(6) M-1 X s-1 at 0 degree C in 50 mM-Tris/HCl, pH 9.0, was obtained. Carbamoyl phosphate, a substrate of ornithine transcarbamoylase, protected the enzyme from inactivation. A dissociation constant of 3 microM for the enzyme-carbamoyl phosphate complex was calculated. L-Ornithine, the second substrate for ornithine transcarbamoylase, protected the enzyme only at high concentrations. The results are consistent with N delta-(N'-sulpho-diaminophosphinyl)-L-ornithine being a potent affinity label that binds via the carbamoyl phosphate-binding site of ornithine transcarbamoylase. Cleavage of phaseolotoxin to N delta-(N'-sulpho-diaminophosphinyl)-L-ornithine in vivo appears to be an important function in the physiology of the disease.

Binding Sites↗
PubMed1985

Stimulation of ethylene production in bean leaf discs by the pseudomonad phytotoxin coronatine.

Coronatine is a toxin produced by Pseudomonas syringae pv. glycinea which induces the same chlorotic response in bean leaves as does infection by the bacterial pathogen. Although the structure of coronatine is known, the biological mode of action is not. One possible clue to its activity is the ethyl-substituted cyclopropane side chain of the molecule. This part structure (1-amino-2-ethycyclopropane-1-carboxylic acid or AEC) is an analog of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC).When coronatine was applied to bean leaf discs in solution, or to intact leaves through prick application, a substantial stimulation of ethylene production was measured. This stimulation was concomitant with an increase in ACC content of the tissue, and occurred under the same conditions as did the chlorotic response to the toxin. The stimulation of ethylene production was inhibited by aminoethoxyvinylglycine, an inhibitor of ACC synthesis. These results, along with those of experiments using l-[U-(14)C]methionine, indicated that the stimulation involved de novo production of ethylene via the methionine pathway.The whole, unhydrolyzed coronatine molecule is probably necessary to elicit both the ethylene and chlorosis responses since neither hydrolysis product (coronafacic acid and coronamic acid AEC]) is effective alone. A naturally occurring analog of coronatine, coronafacoylvaline, also stimulated ethylene production and caused chlorosis. However, the unrelated pseudomonad phytotoxin phaseolotoxin, which also causes chlorosis, did not stimulate ethylene production. Ethylene thus may have a specific role in the coronatine toxic syndrome.

Journal Article↗
PubMed1985

Association between Symptom Development and Inhibition of Ornithine Carbamoyltransferase in Bean Leaves Treated with Phaseolotoxin.

The chlorosis symptom that characterizes the halo blight disease of Phaseolus vulgaris L. is caused by phaseolotoxin produced by the plant pathogenic bacterium Pseudomonas syringae pv phaseolicola. Phaseolotoxin is hydrolyzed by plant peptidases to N(delta)(N'-sulpho-diaminophosphinyl) -l-ornithine which also causes chlorosis and is reported to be an irreversible inhibitor of ornithine carbamoyltransferase (OCTase). We have examined the hypothesis that inhibition of OCTase is the primary action of phaseolotoxin that leads to chlorosis.Chlorotic spots appeared on the primary leaves of P. vulgaris seedlings during the 2 days following leaf prick application of a minimum of 30 picomole phaseolotoxin. OCTase in extracts of the lesions was reduced to 20%, or less, of the activity in controls. Four hours after the application of phaseolotoxin the concentration of free ornithine increased more than 2-fold. Other amino acids, especially glutamine and asparagine-but not arginine-increased later. Chlorophyll remained at a constant level in the phaseolotoxin-treated tissue and the appearance of chlorosis was due to the increase in chlorophyll in the surrounding unaffected tissue.Clear halo symptoms developed only on primary leaves of the youngest seedlings (treated 6-7 days after germination). Lesions did not develop on primary leaves of seedlings more than 14 days old, in which the chlorophyll concentration had reached a maximum. OCTase also was inhibited in the symptomless tissue from older leaves treated with phaseolotoxin, but there was no accumulation of amino acids, including ornithine. A single appliction of 200 nanomoles arginine resulted in the complete regreening of the chlorosis caused by phaseolotoxin. Soluble protein was lower in the chlorotic tissue than in the controls, but increased to greater than the control value following the appliction of arginine. These results suggest that phaseolotoxin-induced chlorosis results from reduced chlorophyll synthesis that is associated with arginine-starvation in the tissue where OCTase is inhibited.

Journal Article↗
PubMed1984

Prediction of subsequent ischemic heart disease using serial resting electrocardiograms.

To test the hypothesis that subtle changes in the resting electrocardiogram can have predictive value for subsequent cardiovascular disease, the authors evaluated serial electrocardiograms from a cohort of initially healthy men and related these to later development of ischemic heart disease. The cohort of 1056 men originally physically qualified for naval aviation were followed from 24-61 years of age between 1940 and 1977. Resting electrocardiograms were obtained at 24, 36, 42, and 54 years of age. Particular emphasis was directed to measurement of electrocardiographic intervals, amplitudes, and vectorial orientation. The potential effects of weight, blood pressure, and other major risk factors on electrocardiographic changes were controlled in analysis. At younger ages, the amplitude of the T wave in lead 2 and the change in P-R interval were predictive of cardiovascular disease. With aging of the cohort, more leftward orientation of the frontal plane QRS and T forces were predictive, as were the serial changes in the angle between QRS and T. When major risk factors (smoking, blood pressures, and serum cholesterol) were included in a predictive model, addition of electrocardiographic changes significantly improved prediction of ischemic heart disease. These subtle serial changes may be helpful to epidemiologists and clinical investigators in assessing risk of subsequent cardiovascular disease.

Adult↗
PubMed1984

Herbal medicine.

Explore the source record for details and available documents.

Europe↗
PubMed1983

Effect of alcohol intake on high-density lipoprotein cholesterol levels in runners and inactive men.

Plasma high-density lipoprotein cholesterol (HDLC) level was measured before and after alcohol abstinence and after resumption of a controlled alcohol dose in 16 marathon runners, 15 joggers, and 13 inactive men. A three-week period of abstinence resulted in a significant decrease in HDLC concentration in the inactive men (49.8 to 41.8 mg/dL). Three weeks of alcohol consumption (1,065 mL of beer per day) produced a significant increase in HDLC level to 50.9 mg/dL. No change in HDLC level was found for the marathon group or the joggers during abstinence or three weeks of alcohol intake. The consumption of alcohol in moderation seems to be associated with increased HDLC levels in inactive men but not in men who engage in regular running or jogging.

Adult↗
PubMed1983

Solomon Islander skin pigmentation: ultrastructural differences related to genetic variation in Melanesia.

Genetic differences between Solomon Islander populations are distinguishable on the basis of melanosome packaging in epidermal keratinocytes. By electron microscopic study of skin pigmentation in various Melanesian populations, we have found distinct inter-island differences in the mode of melanosome packaging. Melanosomes are found as singlets in the skin of Bougainville Islanders but are found aggregated in melanosome complexes in Malaita Islanders and Ontong Javanese. This variation in melanosome packaging represents an important biologic difference found between Solomon Islanders and may reflect the genetic diversity existing in the original Melanesian founding population or the genetic diversity existing in the original Melanesian founding population or populations.

Genetic Variation↗
PubMed1983

Coping with domestic violence: social support and psychological health among battered women.

This study suggests a conceptual framework for examining the impact of stress (i.e., level of violence), personal resources, social support, institutional responsiveness, and coping upon the psychological health (i.e., depression, mastery, and self-esteem) of battered women. Respondents were 60 women who had sought assistance from a shelter for battered women. Results indicated that increased levels of violence, minimal personal resources, lack of institutional and informal social support, and greater avoidant coping styles were related to lowered self-esteem and more severe depressive symptoms. Exploratory analyses suggested that stress (i.e., level of violence) and personal resources may have indirect effects upon functioning through their impact on coping responses and the availability of social support. In particular, women who had fewer social contacts unaccompanied by their partner were less likely to receive supportive responses from friends. Implications for research and practice are discussed.

Adaptation, Psychological↗
PubMed1983

The relationship of exercise and diet on high-density lipoprotein cholesterol levels in women.

The relationship of exercise and diet on high-density lipoprotein (HDL) cholesterol was investigated in 45 long-distance runners (LD), 49 joggers (J), and 47 inactive (I) women. Fasting plasma triglycerides (TG), HDL cholesterol, total cholesterol (TC), and percent body fat (%BF) were measured in women ages 24-58 yr. TG levels were significantly lower in LD compared to I (p less than 0.02). Although TC was not significantly different among groups, HDL-cholesterol was higher in LD (78 mg/dl) compared to J (70 mg/dl) or I (62 mg/dl) (p less than 0.001). Multiple regression analyses indicated that alterations of plasma lipids and lipoprotein levels could not be attributed to intake differences of nutrients. Distance run and %BF were the strongest predictors of HDL-cholesterol in women. LD (23 %BF) were leaner than J (26 %BF) or I (30 %BF); however, when results were adjusted for %BF, significant differences between exercise groups remained for HDL cholesterol.

Adult↗