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D Leong

Publications and source records attributed to D Leong.

At least 37 records · Page 2Linked to original sources
PubMed1989

Maternity care as an essential public service: a proposed role for state government.

This paper describes some of the current problems in assuring basic maternity care as an essential community service in the rural state of Vermont. Solving the cost of care problem will still leave large gaps in the ability of our maternity care system to provide continuous and high-quality maternity care for all pregnant women. The problem of access is not only a temporary aberration of the current medical care system, but a central and identifying characteristic of it. Maternity care services are as essential as other community services such as utilities and education. The authors propose that the state should assure the availability and quality of maternity care services as it would other essential services. The development of a statewide care system using a nurse midwife model of services is suggested.

Female↗
PubMed1988

Characterization of a second gene involved in bacterio-opsin gene expression in a halophilic archaebacterium.

Southern blot analysis and nucleotide sequencing of DNA from three bacterio-opsin-deficient mutants of the archaebacterium Halobacterium halobium (M86, W105, and W109) revealed that they each contain an alteration in a region 2,000 to 3,800 base pairs (bp) upstream of the bacterio-opsin gene (bop). Nucleotide sequence analysis of this region, which is also located downstream of the previously characterized brp gene, revealed that it contains an open reading frame (ORF) of 2,022 bp. This 2,022-bp ORF has a start codon which overlaps the stop codon of the brp gene and is read in the same direction. The ORF could encode an acidic protein of 73,334 daltons (674 amino acids) with a predicted secondary structure typical of a soluble protein. Bop mutant M86 contains a 1,883-bp deletion extending from bp 351 of the ORF, to 197 bp beyond the stop codon. Mutant W105 has an ISH2 element integrated at bp 1239 of the ORF, and mutant W109 has an ISH26 element integrated at bp 1889. Our results suggest that the ORF is a gene (designated bat for bacterio-opsin activator gene) involved in bop gene expression.

Amino Acid Sequence↗
PubMed1988

Transcription of genes involved in bacterio-opsin gene expression in mutants of a halophilic archaebacterium.

Recent studies on the regulation of the bacterio-opsin (bop) gene of the archaebacterium Halobacterium halobium suggest that the brp and putative bat genes are involved in bop gene expression or purple membrane assembly. These two genes are located 526 and 1,602 base pairs, respectively, upstream of the bop gene and are both transcribed in the opposite orientation to the bop gene. Transcription of the bop, brp, and putative bat genes was characterized in the wild type, 11 Bop mutants, and a Bop revertant by using a series of RNA probes. Quantitation of the relative mRNA levels for these three genes in the wild type revealed that the brp and bat transcripts are present at approximately 2 and 4%, respectively, of bop mRNA levels under the growth conditions used. Northern (RNA) blot analysis of Bop mutants indicated that insertions in the brp gene affect expression of the putative bat gene. In addition, deletion of most of the bat gene resulted in virtually undetectable levels of bop and brp mRNAs. These and other results lead us to propose that (i) brp gene expression can affect bat gene expression and (ii) the putative bat gene is involved in activating bop and brp gene expression.

Bacteriorhodopsins↗
PubMed1987

Cold provocation test results from a 1985 survey of hard-rock miners in Ontario.

A total of 143 miners, 6 ex-miners, and 42 referents from five mines in northern Ontario were examined with a cold provocation test. The skin temperatures, measured by thermocouples at the tips of the fingers and thumbs were recorded at 5-s intervals throughout the immersion in cold water (10 degrees C) for 10 min and during the recovery period. The finger skin temperature was followed until 99% recovery had occurred as compared to the starting temperature. For the referents and the vibration-exposed subjects, the results by separate stage of the Taylor-Pelmear scale for hand-arm vibration syndrome were compared. There were statistically significant differences in the mean finger temperature at the 50, 75, 90, and 95% recovery times between stages 0, 0T/0N, and stages 1 through 3 combined, as well as significant differences between stages 1, 2, and 3. The mean temperature at 10 min and the mean hyperemia temperature for eight fingers combined were compared between the miners and referents. There were significant differences in the mean temperature at 10 min and in the hyperemia temperature between the referents and miners in stage 0T/0N, as well as between the referents and the miners in stages 1 through 3 combined. For the worst finger (defined as that with the lowest temperature at 10 min) there was an increasing trend towards a lower hyperemia temperature and delay in recovery time from stage 0 to stages 2 and 3 combined.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Characterization of the diphtheria tox transcript in Corynebacterium diphtheriae and Escherichia coli.

Transcription of the tox gene in lysogenic Corynebacterium diphtheriae strains C7(beta tox+), C7 (gamma tox) and the hypertoxigenic PW8 (omega tox+) was analyzed and compared with transcription of the C. diphtheriae tox gene in the recombinant strain Escherichia coli (pDT201). In all cases S1 nuclease mapping localized the 5' terminus of the tox mRNA to a site 8 or 9 base pairs (bp) downstream of a region similar to the -10 consensus sequence of E. coli promoters. In C. diphtheriae the tox transcript was observed only in strains that were grown under iron-limiting conditions; in the presence of excess iron, transcription beyond bp 38 of the tox coding region was not observed. In contrast, in E. coli(pDT201) tox was expressed at equivalent levels in both iron-depleted and iron-supplemented media. The DNA insertion in the tox gene of the nontoxigenic corynephage gamma was found to occur at bp 54 of the tox coding region. The insertion event resulted in the duplication of a 7-bp target sequence, and the ends of the insert were found to constitute an imperfect inverted repeat of approximately 26 bp. Transcription from the tox promoter in C7(gamma tox) was found to initiate at the same nucleotides as in C7(beta tox+), PW8, and E. coli(pDT201) and remained sensitive to iron inhibition. These observations are discussed in relation to the mechanism of iron-mediated regulation of the tox gene.

Base Sequence↗
PubMed1983

Cloned diphtheria toxin fragment A is expressed from the tox promoter and exported to the periplasm by the SecA apparatus of Escherichia coli K12.

The diphtheria toxin fragment A-related polypeptide encoded by the recombinant plasmid pDT201 (Leong, D., Coleman, K. D., and Murphy, J. R. (1983) Science 220, 515-517) and expressed in Escherichia coli K12 was found to have an electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gels corresponding to 28,500 daltons. Immunoprecipitation experiments revealed that the mature form of the fragment A-related polypeptide was exported to the periplasmic compartment of E. coli K12 harboring plasmid pDT201. The polypeptide was sensitive to trypsin "nicking." Following treatment an Mr = 24,000 fragment was released which co-electrophoresed with fragment A of diphtheria toxin. The precursor form (Mr = 31,000) of the fragment A-related polypeptide was found to accumulate in the cytoplasmic fraction of the temperature-sensitive secretion-defective strain of E. coli K12 under nonpermissive conditions. We further demonstrate that a 263-base pair HaeIII fragment of pDT201 which carries the putative diphtheria tox promoter has promoter activity in E. coli K12.

Autoradiography↗
PubMed1983

Cloned fragment A of diphtheria toxin is expressed and secreted into the periplasmic space of Escherichia coli K12.

An 831-base pair segment of the corynebacteriophage beta tox-45 genome encoding fragment A of diphtheria toxin was cloned into plasmid pUC8 in Escherichia coli K12. Strains containing recombinant plasmids expressed the adenosine diphosphate ribosyl transferase activity characteristic of fragment A; this activity could be inhibited by polyvalent antiserum to fragment A as well as by the appropriate monoclonal antibodies to diphtheria toxin. The transferase activity was secreted into the periplasmic space of E. coli. These findings have implications for the future construction of genetically engineered chimeric toxins.

Antibodies, Monoclonal↗
PubMed1978

Metabolism of homologous and heterologous serum proteins in garter snakes (Thamnophis ordinoides).

The half life (T1/2) of serum immunoglobulin (Ig) and albumin from snakes and mammals were determined in both garter snakes (Thamnophis ordinoides) and mice (Mus musculus). Metabolism of serum proteins in snakes was similar to mammalian protein metabolism in that homologous serum albumin had shorter T1/2 (16 days) than IgG (38 days). Also, reptilian and mammalian serum proteins had a relatively longer T1/2 when injected into closely related species. Thus mammalian serum Ig (rabbit gamma globulin (RGG)) had a shorter T1/2 (6.3 days) in snake than did homologous snake IgG (38 days), whereas in mice, RGG had a longer T1/2 (3.8 days) than snake Ig (0.9 days). Differences between metabolism of homologous and heterologous albumins were apparent only in snakes in which the T1/2 of homologous albumin was approximately 8-fold greater than mammalian albumin. These results indicate that metabolism of both Ig and albumin in snakes is regulated by specific receptors whereas albumin receptors have been difficult to demonstrate in mammals. The results of this study suggest that one of the factors determining the metabolism of a protein is its foreignness to the host perhaps because of receptor cross reactions.

Animals↗
PubMed1976

Immune response in the garter snake (Thamnophis ordinoides).

Garter snakes (Thamnophis ordinoides) were immunized with hen egg albumin, human gamma-globulin and Keyhole limpet haemocyanin in Freund's adjuvant. Antibody was consistently detected by radioimmunoelectrophoresis and in three different gamma- and beta-globulin precipitin lines called IgM (approximately or equal to 20S), Ig-1 (approximately or equal to 9S) and Ig-2 (approximately or equal to 8-5S). Early antibody (day 31 after immunization) was frequently Ig-M whereas Ig-2 and especially Ig-1 were detectable for the longest duration (992 days). After immunization with antigen in Freund's adjuvant, Ig-1 serum concentration showed the greatest increase, from almost undetectable levels to the most prominent immunoglobulin in immune serum.

Animals↗
PubMed1970

Some structural and biological properties of Brucella endotoxin.

Hot phenol-water extraction of smooth Brucella abortus and B. melitensis cells yielded a toxic fraction which was recovered from the phenol phase (fraction 5). Chemically, fractions 5 from both Brucella species were lipid-carbohydrate-protein-2 keto-3-deoxyoctulosonic acid complexes which were stable to heat and resistant to Pronase digestion. Electron micrographs of the Brucella toxins were morphologically indistinguishable from those of enterobacterial endotoxins. Biologically, Brucella toxins were lethal for mice and immunogenic for rabbits. An intravenous injection of Brucella toxin induced severe leukopenia with subsequent leukocytosis in mice. Cross-tolerance experiments with mice demonstrated that pretreatment with B. abortus toxin lessened the hypoferremia produced by challenge with Escherichia coli endotoxin. Furthermore, fractions 5 from B. abortus and B. melitensis were able to form hybrids with E. coli and Salmonella enteritidis endotoxins and also with each other. Although Brucella toxins possess many structural and biological properties in common with endotoxins from the Enterobacteriaceae, some quantitative differences in their biological potencies were observed. Brucella toxins were relatively innocuous in tests for pyrogenicity in rabbits and lethality for chick embryos. In nonspecific protection tests, Brucella toxin had only 1/75 the potency of E. coli endotoxin in protecting mice against challenge with virulent S. typhi. However, on the basis of the data presented and on the work done previously, we concluded that the heat-stable toxins of B. abortus and B. melitensis were endotoxins.

Journal Article↗
PubMed1969

Distribution of chromate-labeled Brucella abortus endoxin in tolerant mice.

Endotoxin tolerance as manifested by a lesser degree of hypoferremia was demonstrated in mice when both pretreatment (10 mug per injection) and challenge (100 mug) does of Brucella abortus endotoxin were administered intraperitoneally. Qualitative and quantitative studies on the distribution of chromate-labeled endotoxin in normal mice revealed that the endotoxin localized predominately in the liver and hypoferremia could be related to a high uptake of endotoxin by this organ. In tolerant mice, the labeled endotoxin was found mainly in the mesenteric lymph nodes (MLN) with smaller quantities in the blood, spleen, and liver. Experiments with splenectomized mice provided supporting evidence that the liver was the target organ of the hypoferremic response to endotoxin. High localization of endotoxin in the MLN with lower quantities in the blood, livers, and spleens of tolerant mice indicated that tolerance may be the result of a blockage by the MLN, preventing the endotoxin from reaching the liver. This inference was supported by the finding that hypoferremic tolerance did not occur when the hypoferremia-provoking dosage of endotoxin (100 mug) was given intravenously to mice pretreated intraperitoneally. There was less hypoferremia in normal mice injected with a mixture of antiserum and 100 mug of endotoxin than in mice given the same dosage of endotoxin in saline. Distribution studies on endotoxin treated with specific antiserum revealed that the endotoxin localized principally in the MLN, thus preventing most of the endotoxin from reaching the liver, the target organ of the hypoferremic response.

Animals↗
PubMed1968

Identification of the toxic component of Brucella abortus endotoxin and its labeling with radioactive chromate.

The evidence obtained from immuno-gel diffusion, centrifugation, and toxicity studies employing the serum iron assay proved that most of the toxicity in an ether-water brucella endotoxin preparation lies in the slow-diffusing component identified as the biologically active endotoxin. Subsequent destruction of the slow-diffusing component by acid hydrolysis resulted in a corresponding loss of toxicity. Chromate-51 was found to attach almost entirely on the slow-diffusing biologically active component and, hence, is a valid label for endotoxin derived from smooth Brucella abortus by the ether-water method.

Animals↗
PubMed1968

Taxonomic position in the genus Brucella of the causative agent of canine abortion.

The gram-negative organism causing abortion in dogs was examined in parallel with cultures representative of the Brucella species and with Bordetella bronchiseptica. The organism fits into the genus Brucella and most closely resembles B. suis on the basis of its growth characteristics. It is of rough colonial morphology and is agglutinated by antisera prepared against rough Brucella. In mouse toxicity tests, no endotoxic activity could be demonstrated. In contrast to most Brucella cultures, it does not utilize erythritol. Electron microscopy showed a cell wall structure similar to that of other gram-negative organisms. The question of whether the organism should be designated Brucella canis, as proposed by Carmichael and Bruner, or Brucella suis biotype 5 is discussed. The authors favor the designation Brucella canis because the organism lacks the lipopolysaccharide antigen associated with the smooth agglutinogen and endotoxin, and it does not utilize erythritol.

Abortion, Veterinary↗
PubMed1968

Surface antigens of smooth brucellae.

Surface antigens of smooth brucellae were extracted by ether-water, phenol-water, trichloroacetic acid, and saline and examined by immunoelectrophoresis and gel diffusion with antisera from infected and immunized rabbits. Ether-water extracts of Brucella melitensis contained a lipopolysaccharide protein component, which was specific for the surface of smooth brucellae and was correlated with the M agglutinogen of Wilson and Miles, a polysaccharide protein component devoid of lipid which was not restricted to the surface of smooth brucellae and was not correlated with the smooth agglutinogen (component 1), and several protein components which were associated with internal antigens of rough and smooth brucellae. Immunoelectrophoretic analysis of ether-water extracts of B. abortus revealed only two components, a lipopolysaccharide protein component, which was correlated with the A agglutinogen, and component 1. Component 1 from B. melitensis and B. abortus showed identity in gel diffusion tests, whereas component M from B. melitensis and component A from B. abortus showed partial identity with unabsorbed antisera and no cross-reactions with monospecific sera. Attempts to prepare monospecific sera directly by immunization of rabbits with cell walls or ether-water extracts were unsuccessful. Absorption of antisera with heavy fraction of ether-water extracts did not always result in monospecific sera. It was concluded (as has been described before) that the A and M antigens are present on a single antigenic complex, in different proportions depending upon the species and biotype, and that this component is a lipopolysaccharide protein complex of high molecular weight that diffuses poorly through agar gel. Components 1, A, and M were also demonstrated in trichloroacetic acid and phenol-water extracts. With all extracts, B. melitensis antigen showed greater diffusibility in agar than B. abortus antigens. After mild acid hydrolysis, B. abortus ether-water extract was able to diffuse more readily.

Agglutination Tests↗