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Biomedical subjects

S Wolfe

Publications and source records attributed to S Wolfe.

At least 55 records · Page 3Linked to original sources

Ethics and equity in Canadian health care: policy alternatives.

Four interrelated phenomena are at work in Canadian health care. First, in Canada as all over the world, there is growing momentum toward greater cost containment and imposition of tighter ceilings on health expenditures. Second is the demography of a falling birth rate and a greater number of elderly. Third, the failure of ratification by the provinces of the Canadian Meech Lake accord has created a constitutional structure that strongly favors provincial and not federal powers, and further guarantees widened regional and local disparities. Fourth, the economic union implicit in the United States-Canada free trade agreement of late 1988 will serve to weaken east-west ties within Canada in favor of north-south ties, and is likely to lead to taxation policy in Canada to favor the rich, with pressures toward privatization and restrictions on universal entitlement programs.

Canada↗

Oxygen derepresses deacetoxycephalosporin C synthase and increases the conversion of penicillin N to cephamycin C in Streptomyces clavuligerus.

When dissolved oxygen (DO) was maintained at saturation level during batch fermentations of Streptomyces clavuligerus (NRRL 3585), the accumulation of the intermediate penicillin N was lowered while formation of the end product cephamycin C was increased relative to fermentations without DO control. The specific activity of the penicillin ring-expansion enzyme deacetoxycephalosporin C synthase (DAOCS) was increased 2.3-fold under oxygen saturated conditions, whereas the penicillin ring-cyclizing enzyme isopenicillin N synthase (IPNS) showed only a 1.3-fold increase. Thus oxygen derepression of DAOCS appears to be an important regulatory mechanism in the conversion of penicillin N to cephamycin C in S. clavuligerus. IPNS, an early acting enzyme in cephamycin C biosynthesis, and DAOCS, which acts late in the pathway, both disappeared from cell extracts at 60 h, just prior to cessation of cephamycin production.

Cephamycins↗

Cosegregation of the renin allele of the spontaneously hypertensive rat with an increase in blood pressure.

The spontaneously hypertensive rat (SHR) exhibits alterations in the renin-angiotensin-aldosterone system which are similar to those that characterize patients with "nonmodulating" hypertension, a common and highly heritable form of essential hypertension. Accordingly, we determined whether the inheritance of a DNA restriction fragment length polymorphism (RFLP) marking the renin gene of the SHR was associated with greater blood pressure than inheritance of a RFLP marking the renin gene of a normotensive control rat. In an F2 population derived from inbred SHR and inbred normotensive Lewis rats, we found the blood pressure in rats that inherited a single SHR renin allele to be significantly greater than that in rats that inherited only the Lewis renin allele. To the extent that the SHR provides a suitable model of "nonmodulating" hypertension, these findings raise the possibility that a structural alteration in the renin gene, or a closely linked gene, may be a pathogenetic determinant of increased blood pressure in one of the most common forms of essential hypertension in humans.

Alleles↗

Measurement of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase activity in Streptomyces clavuligerus by high-performance liquid chromatography after precolumn derivatization with o-phthaldialdehyde.

A procedure for rapid, sensitive measurement of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) in complex cell extracts has been developed by adapting a widely used method for high-performance liquid chromatography analysis of amino acids. Samples were oxidized with performic acid and derivatized with o-phthaldialdehyde-mercaptoethanol to give the fluorescent isoindole derivative of the peptide sulfonate. The procedure was used to assay Streptomyces clavuligerus cell extracts and partially purified fractions for ACV synthetase activity and to determine some characteristics of the enzyme reaction. The presence of a second enzyme with cysteine as a substrate was also indicated.

Chromatography, High Pressure Liquid↗

Phosphate regulation of ACV synthetase and cephalosporin biosynthesis in Streptomyces clavuligerus.

Cephalosporin production by Streptomyces clavuligerus was reduced sharply by 60 mM phosphate added to a chemically-defined medium. All the four synthetases in the pathway examined, i.e., ACV synthetase, cyclase, epimerase and expandase, were repressed by phosphate, with ACV synthetase being the main repression target and expandase the next. ACV synthetase activity was inhibited by phosphate to a lesser extent than expandase and cyclase, and this inhibition could be reversed by adding Fe2+. Fe2+ itself was inhibitory to ACV synthetase action.

Cephalosporins↗

Imaging of the nontraumatic acute abdomen.

Plain-film radiography of the abdomen is often the first-line imaging modality used for the patient in the ED. It is capable of demonstrating abnormal locations of gas, abnormal viscera, calcifications and foreign material, and skeletal and lower lung pathology. PFR findings may aid in the decision to proceed to other modalities. Contrast studies have a limited role in the ED but may be necessary to diagnose disease inadequately visualized by PFR, as in the case of perforated duodenal ulcer, missed on PFR in approximately 15 per cent of cases. Ultrasound is most useful in the ED for obstetric and gynecologic illness, as well as disorders of the hepatobiliary system. Nuclear medicine studies can be very useful for GI bleeding and inflammatory conditions but may not always be as available or convenient as other modalities. CT has very broad usefulness. Angiography is very useful for locating bleeding sites, especially in the large bowel, and for determination of mesenteric arterial patency in suspected mesenteric ischemia. Finally, MRI, which has enormous potential, is not funded by many third-party payment plans for use in emergencies, and must overcome certain obstacles before it assumes common usage in the ED.

Abdomen, Acute↗

Cocaine binding at sigma receptors.

Cocaine and some related psychostimulants interact with sigma receptors in binding assays. Their Ki values are compatible with blood concentrations reported to produce psychosis in human volunteers. It is proposed that the psychotomimetic effects of some psychostimulants may derive, at least in part, from their interaction with sigma receptors.

Animals↗

Cloning and nucleotide sequence determination of the isopenicillin N synthetase gene from Streptomyces clavuligerus.

The isopenicillin N synthetase (IPNS) gene from Streptomyces clavuligerus was isolated from an Escherichia coli plasmid library of S. clavuligerus genomic DNA fragments using a 44-mer mixed oligodeoxynucleotide probe. The nucleotide sequence of a 3-kb region of the cloned fragment from the plasmid, pBL1, was determined and analysis of the sequence showed an open reading frame that could encode a protein of 329 amino acids with an Mr of 36,917. When the S. clavuligerus DNA from pBL1 was introduced into an IPNS-deficient mutant of S. clavuligerus on the Streptomyces vector pIJ941, the recombinant plasmid was able to complement the mutation and restore IPNS activity. The protein coding region of the S. clavuligerus IPNS gene shows about 63% and 62% similarity to the Cephalosporium acremonium and Penicillium chrysogenum IPNS nucleotide sequences, respectively, and the predicted amino acid sequence of the encoded protein showed about 56% similarity to both fungal sequences.

Acremonium↗

Indoxyl-beta-D-glucuronide, a novel chromogenic reagent for the specific detection and enumeration of Escherichia coli in environmental samples.

About 97% of Escherichia coli strains produce beta-glucuronidase, but almost all other Enterobacteriaceae lack this enzyme. A D-glucopyranosiduronic acid (glucuronide) possessing a readily detectable beta-linked aglycone should, therefore, constitute a specific reagent for the detection of this organism. For this purpose, the title compound has been synthesized for the first time. The synthesis proceeds in eight steps from readily available D-glucuronolactone, anthranilic acid, and chloroacetic acid and can be carried out on a large scale. The compound has the predicted properties: when included in the standard membrane filter test for the analysis of water, indoxyl-beta-D-glucuronide allows specific detection of E. coli through the formation of blue colonies that are the result of rapid conversion of the liberated aglycone to indigo. The recovery of E. coli is easily measured and almost quantitative.

Chemical Phenomena↗

Purification and initial characterization of deacetoxycephalosporin C synthase from Streptomyces clavuligerus.

Deacetoxycephalosporin C synthase, the penicillin N ring expansion enzyme from Streptomyces clavuligerus, was purified to near homogeneity, as judged by sodium dodecyl sulphate - polyacrylamide gel electrophoresis. The synthase was monofunctional and could be completely separated from deacetoxycephalosporin C hydroxylase activity early in the purification sequence. Synthase specific activity was increased 97-fold over crude cell-free extracts, and the purified enzyme appeared to be a monomer with a molecular weight of 36,000 and a Km for the penicillin N substrate of 50 microM. Deacetoxycephalosporin C synthase activity required alpha-ketoglutarate, Fe2+, and oxygen and was specifically stimulated by ascorbate and dithiothreitol. The enzyme was sensitive to thiol-specific inhibitors, the most effective of which was N-ethylmaleimide.

Chromatography, Ion Exchange↗

Community hospital administration of intravenous tissue plasminogen activator in acute myocardial infarction: improved timing, thrombolytic efficacy and ventricular function.

As an investigational fibrinolytic agent for acute myocardial infarction, intravenous recombinant tissue-type plasminogen activator (rt-PA) has been administered primarily in tertiary care and university centers. To determine the value of early initiation of such therapy, two satellite community hospital emergency rooms were established for use of rt-PA and the experience was compared among 142 consecutive patients who were transferred to a regional center for acute cardiac catheterization after intravenous rt-PA therapy. In Group I (n = 19), patients received rt-PA after interhospital transport to the regional center, but before cardiac catheterization. In Group II (n = 70), rt-PA therapy was initiated by the helicopter physician and nurse team after their arrival at the local community hospital emergency room. Group III patients (n = 53) had rt-PA administered in the local community hospital by the emergency room physician. Group III patients had earlier initiation of therapy (2.1 +/- 0.8 hours in Group III versus 3.8 +/- 1.2 hours in combined Groups I and II, p less than 0.001) and an increased rate of infarct vessel recanalization on the 90 minute coronary angiogram (81 in Group III versus 67% in combined Groups I and II, p = 0.057). The patients in Group III had a higher acute left ventricular ejection fraction (54 +/- 8% versus 50 +/- 9.5% in combined Groups I and II, p less than 0.01) and a trend toward an increased 7 day ejection fraction (55.5 +/- 9% versus 51.7 +/- 9.5%, respectively, p = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Catheterization↗

Effect of ammonium as nitrogen source on production of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase by Cephalosporium acremonium C-10.

Cephalosporin production by Cephalosporium acremonium strain C-10 was suppressed when the organic nitrogen source (1.2% L-asparagine) was replaced by 1.2% (NH4)2SO4. A higher level of (NH4)2SO4 (3.5%) led to even greater suppression. Ammonium repression was exerted on formation of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase, together with that of expandase; a lesser effect by ammonium was observed on cyclase production. Inhibition of ACV synthetase activity byammonium was also observed (ca. 50% inhibition at 250 mM NH4+).

Acremonium↗

Cell-free synthesis of delta-(L-alpha-aminoadipyl)-L-cysteine, the first intermediate of penicillin and cephalosporin biosynthesis.

delta-(L-alpha-aminoadipyl)-L-cysteine synthetase (LL-AC synthetase) activity has been found in extracts of Cephalosporium acremonium C-10. The enzyme extract carries out a linear synthesis of LL-AC from its constituent amino acids for at least 6 hours. The reaction is dependent on active enzyme, time, L-alpha-aminoadipate, L-cysteine, ATP and Mn2+ or Mg2+. The activity is stabilized by glycerol.

Acremonium↗

Relationship between nitrogen assimilation and cephalosporin synthesis in Streptomyces clavuligerus.

The levels of three enzymes of the beta-lactam antibiotic pathway and overall cephalosporin production were subject to nitrogen source repression in Streptomyces clavuligerus. The specific activities of isopenicillin N synthetase ("cyclase") and deacetoxycephalosporin C synthetase ("expandase") measured during the exponential phase depended on the nitrogen source employed, following a pattern that roughly correlated with the corresponding antibiotic production. The effects on isopenicillin N epimerase ("epimerase") activities were less marked than those on the cyclase and expandase. Production of cephalosporins and enzymatic activities were not related to the growth rate of the cultures. Glutamate, glutamine and alanine inhibited production when added to resting cell systems, while lysine and alpha-aminoadipate were stimulatory. No clear relationship could be drawn between cephalosporin production or beta-lactam synthetase activities and the activities of enzymes of ammonium assimilation (glutamine synthetase, glutamate synthase and alanine dehydrogenase). The intracellular pools of free glutamine, alanine and ammonium were the only ones markedly affected by the nitrogen source in the wild type and mutants, but these amino acids did not seem to play an obvious role as intracellular mediators of nitrogen control.

Alanine Dehydrogenase↗

Purification of isopenicillin N synthetase from Streptomyces clavuligerus.

Isopenicillin N synthetase was purified from Streptomyces clavuligerus by sequential salt precipitation, ion-exchange and gel-filtration chromatography using both conventional open column and high-performance liquid chromatographic techniques. Material from the final purification step had a specific activity of 204.1 X 10(-3) units/mg of protein which represented a 130-fold purification over the cell-free extract. The purified isopenicillin N synthetase was determined to have a molecular weight of 33,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and to have a Km of 0.32 mM with respect to its substrate delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine. The enzyme showed a sensitivity to thiol-specific inhibitors with N-ethylmaleimide giving the strongest inhibitory effect.

Chromatography, Gel↗