Roles of novobiocin-sensitive topoisomerases in chloroplast DNA replication in Chlamydomonas reinhardtii.

We have examined DNA replication in Chlamydomonas reinhardtii chloroplasts in vivo when chloroplast type II topoisomerases are inactivated with sublethal doses of novobiocin. DNA replication is at first inhibited under these conditions. However, after a delay of several hours, chloroplast chromosomes initiate a novobiocin-insensitive mode of DNA replication. This replication starts preferentially near a hotspot of recombination in the large inverted repeats, instead of from the normal chloroplast origins, oriA and oriB. It replicates one, but not the other single-copy region of the chloroplast chromosome. We speculate that novobiocin-insensitive DNA replication in chloroplasts requires recombination in this preferred initiation region.     

Medical direction and control of emergency medical services in Canada.

OBJECTIVE: To determine the level of physician involvement in prehospital emergency medical services (EMS) in Canada, as compared with published principles of medical control and direction. DESIGN: Mail and telephone survey by means of a questionnaire from March to November 1991. SETTING: All Canadian provinces and territories. PARTICIPANTS: Fifty-six key prehospital EMS physicians, senior government administrators and senior representatives of the agencies responsible for licensing physicians in each province or territory. MAIN OUTCOME MEASURES: Responses to questions regarding the legislation, organization, administration, practice and regulation of medical direction and control by physicians in each province or territory. RESULTS: EMS legislation describing medical direction and control was completely lacking in five provinces and both territories and was incomplete in the remainder. Provincial guidelines written by physicians for prehospital patient care were present in only four provinces. Formal organization of medical directors varied from none to partially remunerated networks. Regional medical-director systems were present in three provinces, and local medical directors were required for all communities in three. Most rural ambulance services were found to engage physicians only when there was local interest. CONCLUSIONS: The level of physician involvement in the medical direction and control of EMS appears to be inconsistent across Canada and insufficient in most jurisdictions, as compared with accepted principles.     

Characterization of a cell surface adhesion molecule expressed by a subset of developing chick neurons.

We have isolated a 105-kDa membrane glycoprotein expressed by subsets of developing chick neurons. This glycoprotein, identified by the JC7 monoclonal antibody, is present on the surface of axons and cell bodies of developing spinal motor neurons, dorsal root ganglion sensory neurons, sympathetic and parasympathetic neurons, and a small subset of brain neurons. Late in development the JC7 antigen is expressed at high levels on CNS nonneuronal glial-like cells. When attached to latex beads this glycoprotein can mediate homophilic adhesion and when used as a culture substrate stimulates a highly branched pattern of neurite outgrowth from dorsal root ganglion explants. The JC7 antigen appears to be identical to the SC1, BEN, and DM antigens. Its limited distribution, adhesive qualities, and ability to stimulate neurite outgrowth suggest it may play a role in the selective growth of neural processes during development.     

Costs and cost effectiveness of cardiovascular screening and intervention: the British family heart study.

OBJECTIVE--To measure costs and cost effectiveness of the British family heart study cardiovascular screening and intervention programme. DESIGN--Cost effectiveness analysis of randomised controlled trial. Clinical and resource use data taken from trial and unit cost data from external estimates. SETTING--13 general practices across Britain. SUBJECTS--4185 men aged 40-59 and their 2827 partners. INTERVENTION--Nurse led programme using a family centered approach, with follow up according to degree of risk. MAIN OUTCOME MEASURES--Cost of the programme it self; overall short term cost to NHS; cost per 1% reduction in coronary risk at one year. RESULTS--Estimated cost of putting the programme into practice for one year was 63 pounds per person (95% confidence interval 60 pounds to 65 pounds). The overall short term cost to the health service was 77 pounds per man (29 pounds to 124 pounds) but only 13 pounds per woman (-48 pounds to 74 pounds), owing to differences in utilisation of other health service resources. The cost per 1% reduction in risk was 5.08 pounds per man (5.92 pounds including broader health service costs) and 5.78 pounds per woman (1.28 pounds taking into account wider health service savings). CONCLUSIONS--The direct cost of the programme to a four partner practice of 7500 patients would be approximately 58,000 pounds. Annually, 8300 pounds would currently be paid to a practice of this size working to the maximum target on the health promotion bands, plus any additional reimbursement of practice staff salaries for which the practice qualified. The broader short term costs to the NHS may augment these costs for men but offset them considerably for women.     

Peroxynitrite-Induced Cytotoxicity in PC12 Cells: Evidence for an Apoptotic Mechanism Differentially Modulated by Neurotrophic Factors

Abstract: Peroxynitrite is a powerful oxidant formed by the near-diffusion-limited reaction of nitric oxide with superoxide. Large doses of peroxynitrite (>2 m M ) resulted in rapid cell swelling and necrosis of undifferentiated PC12 cells. However, brief exposure to lower concentrations of peroxynitrite (EC₅₀ = 850 µ M ) initially (3–4 h) caused minimal damage to low-density cultures. By 8 h, cytoplasmic shrinkage with nuclear condensation and fragmentation became increasingly evident. After 24 h, 36% of peroxynitrite-treated cells demonstrated these features associated with apoptosis. In addition, 46% of peroxynitrite-treated cells demonstrated DNA fragmentation (by terminal-deoxynucleotide transferase-mediated dUTP-digoxigenin nick end-labeling) after 7 h, which was inhibited by posttreatment with the endonuclease inhibitor aurintricarboxylic acid. Serum starvation also resulted in apoptosis in control cells (23%), the percentage of which was not altered significantly by peroxynitrite treatment. Although peroxynitrite is known to be toxic to cells, the present study provides a first indication that peroxynitrite induces apoptosis. Furthermore, pretreatment of cells with nerve growth factor or insulin, but not epidermal growth factor, was protective against peroxynitrite-induced apoptosis. However, both acidic and basic fibroblast growth factors greatly increased peroxynitrite-initiated apoptosis, to 63 and 70%, respectively. Thus, specific trophic factors demonstrate differential regulation of peroxynitrite-induced apoptosis in vitro.     

Phospho-beta-glucosidase from Fusobacterium mortiferum: purification, cloning, and inactivation by 6-phosphoglucono-delta-lactone.

6-Phosphoryl-beta-D-glucopyranosyl:6-phosphoglucohydrolase (P-beta-glucosidase, EC 3.2.1.86) has been purified from Fusobacterium mortiferum. Assays for enzyme activity and results from Western immunoblots showed that P-beta-glucosidase (Mr, 53,000; pI, 4.5) was induced by growth of F. mortiferum on beta-glucosides. The novel chromogenic and fluorogenic substrates, p-nitrophenyl-beta-D-glucopyranoside-6-phosphate (pNPbetaGlc6P) and 4-methylumbelliferyl-beta-D-glucopyranoside-6-phosphate (4MUbetaGlc6P), respectively, were used for the assay of P-beta-glucosidase activity. The enzyme hydrolyzed several P-beta-glucosides, including the isomeric disaccharide phosphates cellobiose-6-phosphate, gentiobiose-6-phosphate, sophorose-6-phosphate, and laminaribiose-6-phosphate, to yield glucose-6-phosphate and appropriate aglycons. The kinetic parameters for each substrate are reported. P-beta-glucosidase from F. mortiferum was inactivated by 6-phosphoglucono-delta-lactone (P-glucono-delta-lactone) derived via oxidation of glucose 6-phosphate. The pbgA gene that encodes P-beta-glucosidase from F. mortiferum has been cloned and sequenced. The first 42 residues deduced from the nucleotide sequence matched those determined for the N terminus by automated Edman degradation of the purified enzyme. From the predicted sequence of 466 amino acids, two catalytically important glutamyl residues have been identified. Comparative alignment of the amino acid sequences of P-beta-glucosidase from Escherichia coli and F. mortiferum indicates potential binding sites for the inhibitory P-glucono-delta-lactone to the enzyme from F. mortiferum.