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Biomedical subjects

M R Jones

Publications and source records attributed to M R Jones.

At least 91 records · Page 5Linked to original sources
PubMed1995

Renovation of a semiprivate patient room. Bowman Center Geriatric Rehabilitation Unit.

A multidisciplinary total quality management (TQM) environment committee was formed to create a more accessible, home-like environment for patients on a geriatric rehabilitation unit. Problems in semiprivate rooms related to wheelchair use and age-related changes in the elderly were identified. After using the TQM process to find solutions to these problems, the committee remodeled two semiprivate rooms. Surveys indicate improvement in accessibility, storage, lighting, appearance, and cleanliness.

Academic Medical Centers↗
PubMed1994

Coherent nuclear dynamics at room temperature in bacterial reaction centers.

A room-temperature study is reported of the femtosecond spectral evolution of the stimulated emission band of the primary electron-transfer precursor P* in bacterial photosynthesis. The study was performed with membranes of the antenna-deficient RCO1 mutant of Rhodobacter sphaeroides. A time-dependent red shift, reflecting nuclear motion out of the Franck-Condon region of the excited state, is resolved. Analysis of oscillatory features persisting for > 1 ps in the kinetics revealed main frequencies of the activated motions at 30, 84, 145, and 192 cm-1. The oscillations occur on the time scale of primary electron transfer. Our results set a lower limit for the vibrational dephasing time in P* that is not compatible with the usual assumption in theoretical treatments of complete vibrational relaxation prior to electron transfer, even at room temperature.

Bacteriochlorophylls↗
PubMed1994

The Rhodobacter sphaeroides PufX protein is not required for photosynthetic competence in the absence of a light harvesting system.

The effects of deletion of the gene encoding the PufX protein from Rhodobacter sphaeroides have been examined using bacterial strains with simplified photosystems. We find that the PufX protein is required for photosynthetic growth in strains which have the LH1 antenna complex, but is not required in a reaction centre-only strain, suggesting that the PufX protein does not directly facilitate cyclic electron transfer between the reaction centre and the cytochrome bc1 complex. The influence of PufX and carotenoid type on the size of the reaction center/LH1 core complex has also been examined in these strains.

Bacterial Proteins↗
PubMed1994

Coherent dynamics during the primary electron-transfer reaction in membrane-bound reaction centers of Rhodobacter sphaeroides.

The temporal evolution of the near-infrared stimulated emission band of the special pair excited state (P*) in the reaction center of Rhodobacter sphaeroides has been studied in intracytoplasmic membranes of the antenna-deficient RCO1 mutant at 10 K with a resolution of 30 fs. On the 100-fs time scale the emission band gradually shifts to longer wavelengths. After 150 fs the band shifts back to shorter wavelengths and continues to develop on the picosecond time scale in a damped oscillatory manner (most prominent fundamental frequencies around 15 cm-1 and at 92, 122, and 153 cm-1). These phenomena are shown to be due to low-frequency vibrational motions in the P* excited state that conserve their phase on the time scale of electron transfer. These results imply that the vibrational manifold of P* is not thermalized during the electron-transfer reaction in functional reaction centers. The initial Stokes shift dynamics are largely determined by the modes in the 90-160-cm-1 frequency range, which probably involve motions of several chromophores, including the bacteriopheophytin electron acceptor HL.

Electron Transport↗
PubMed1994

Trapping kinetics in mutants of the photosynthetic purple bacterium Rhodobacter sphaeroides: influence of the charge separation rate and consequences for the rate-limiting step in the light-harvesting process.

The primary light-harvesting processes, energy transfer in the light-harvesting antenna, and trapping of the excited states by reaction centers were studied in several mutant strains of the photosynthetic purple bacterium Rhodobacter sphaeroides. The mutants had reaction centers in which the rates of electron transfer were modified by site-directed mutations at the M210 position. Low-intensity pump-probe laser spectroscopy was used to monitor the absorbance transients in the Qy region of the antenna pigments, and it was found that despite a wide variation in charge separation rates within the RC, produced by the alterations at Tyr M210, there was relatively little corresponding variation in the overall trapping rate. These effects of the mutations on the trapping kinetics demonstrate that the rate-limiting step of the overall light-harvesting process is the transfer of the excitations from the antenna to the reaction center.

Electrochemistry↗
PubMed1994

Site-specific mutagenesis of the reaction centre from Rhodobacter sphaeroides studied by Fourier transform Raman spectroscopy: mutations at tyrosine M210 do not affect the electronic structure of the primary donor.

The effects of mutation of residue tyrosine M210 on the primary donor bacteriochlorophylls have been investigated by near infrared FT-Raman spectroscopy in reaction centres purified from an antenna-deficient strain of Rhodobacter sphaeroides. We find that mutation at the M210 position does not significantly perturb the distribution of the unpaired electron over the pair of bacteriochlorophyll molecules which constitute the primary donor radical cation. We conclude, therefore, that the effects of mutation of tyrosine M210 on the rate and asymmetry of primary electron transfer in reaction centres cannot be ascribed to a change in the electronic structure of the primary donor.

Bacteriochlorophylls↗
PubMed1994

Etiology of severe malnutrition: results of an international cross-sectional study in continuous ambulatory peritoneal dialysis patients.

In an international cross-sectional study of 224 continuous ambulatory peritoneal dialysis (CAPD) patients, 59% were well nourished but 8% had severe malnutrition. To investigate factors that might underlie the severe malnutrition, we analyzed these data further. Forty-one percent of well-nourished patients had no residual renal function (RRF). Compared with well-nourished patients who had RRF, patients with no RRF received more dialysis, but not enough to compensate completely for loss of RRF. In addition, well-nourished patients with no RRF had a lower protein catabolic rate (PCR) than patients with RRF, although somatic and visceral protein stores were similar in the two groups. Compared with well-nourished patients with no RRF, severely malnourished patients, 94% of whom had no RRF, were prescribed and were receiving a lower total volume of dialysate. The latter had actual body weights (ABWs) that were considerably less than their desirable body weights (DBWs) due to recent losses of somatic protein and fat stores, whereas well-nourished patients were at or near their DBWs. Urea clearance, normalized to 0.58 x ABW, was similar in well-nourished and severely malnourished patients with no RRF, but was significantly decreased in severely malnourished patients when normalized to 0.58 x DBW. This suggests that in severely malnourished patients no compensation had been made for their loss of RRF, and they may have been chronically underdialyzed. The PCR, normalized to ABW, was similar in well-nourished and severely malnourished patients. Thus, the severely malnourished patients were not eating the additional protein that would have been required to restore good protein status.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Sensitivity to event timing in regular and irregular sequences: influences of musical skill.

In two experiments, the performance of listeners with different amounts of musical training (high skill, low skill) was examined in a two-alternative forced choice time-detection task involving simple five-cycle acoustic sequences. In each of a series of trials, all listeners determined which of two pattern cycles contained a small time change. Sequence context was also varied (regular vs. irregular timing). In Experiment 1, in which context was manipulated as a between-subjects variable, high-skill listeners performed significantly better than low-skill listeners only with regular patterns. In Experiment 2, in which context was manipulated as a within-subjects variable, the only significant source of variance was pattern context: All listeners were better at detecting time changes in regular than in irregular patterns. The results are considered in light of several hypotheses, including the expectancy/contrast model (Jones & Boltz, 1989).

Auditory Perception↗
PubMed1993

Direct energy transfer from the peripheral LH2 antenna to the reaction center in a mutant of Rhodobacter sphaeroides that lacks the core LH1 antenna.

The light-harvesting apparatus of the photosynthetic bacterium Rhodobacter sphaeroides is composed of a peripheral LH2 complex which directs excitation energy to the LH1/reaction center core. The puf BA genes encoding the LH1 polypeptides have been deleted, producing a photosynthetically-competent strain which contains LH2 and reaction centers. Time-resolved absorption and fluorescence measurements demonstrate that energy is efficiently transferred from LH2 to the reaction center, despite the absence of LH1. Energy trapping takes place in 55 +/- 5 ps at room temperature, compared to the result for the wild-type strain of 60 +/- 5 ps. At 77 K, the results for the mutant and wild type are 75 +/- 5 and approximately 35 ps, respectively; the slower time in the mutant is attributed to the small differences in antenna/reaction center contacts and relative distances that are bound to exist as a consequence of LH1 and LH2 being assembled from different alpha- and beta-polypeptides. Measurements with closed reaction centers provided new information on the nature of fast energy transfer within the B850 pigments of LH2. We conclude that the absorption band is inhomogeneously broadened, and the fast (approximately 10 ps) lifetime observed in the 847-857-nm region is interpreted as very rapid (1-5 ps) hopping of the excitation energy from high-energy to low-energy pigments within the B850 absorption band. Time-resolved anisotropy studies demonstrate that energy-transfer events within B850 occur on a subpicosecond to picosecond time scale.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy Transfer↗
PubMed1993

Surveillance of poisoning and drug overdose through hospital discharge coding, poison control center reporting, and the Drug Abuse Warning Network.

There is no gold standard for determining poisoning incidence. We wished to compare four measures of poisoning incidence: International Classification of Diseases 9th Revision (ICD-9) principal (N-code) and supplemental external cause of injury (E-code) designations, poison control center (PCC) reporting, and detection by the Drug Abuse Warning Network (DAWN). We studied a case series at two urban hospitals. We assigned ICD-9 N-code and E-code classifications, determining whether these matched with medical records. We ascertained PCC and DAWN system reporting. A total of 724 subjects met entry criteria; 533 were studied (74%). We matched poisoning N-codes for 278 patients (52%), E-code by cause in 306 patients (57%), and E-code by intent in 171 patients (32%). A total of 383 patients (72%) received any poisoning N-code or any E-code. We found that PCC and DAWN reporting occurred for 123 of all patients (23%) and 399 of 487 eligible patients (82%), respectively. In multiple logistic regression, factors of age, hospital admission, suicidal intent, principal poisoning or overdose type, and mixed drug overdose were statistically significant predictors of case match or report varying by surveillance measure. Our findings indicate that common surveillance measures of poisoning and drug overdose may systematically undercount morbidity.

Adolescent↗
PubMed1993

Expected endings and judged duration.

In four experiments, the predictions of an expectancy/contrast model (Jones & Boltz, 1989) for judged duration were evaluated. In Experiments 1 and 2, listeners estimated the relative durations of auditory pattern pairs that varied in contextual phrasing and temporal contrast. The results showed that when the second pattern of a pair either seems to (Experiments 1 and 2) or actually does (Experiment 2) end earlier (later) than the first, subjects judge it as being relatively shorter (longer). In Experiment 3, listeners heard single patterns in which notes immediately preceding the final one were omitted. Timing of the final (target) tone was varied such that it was one beat early, on time, or one beat late. Listeners' ratings of target tones revealed systematic effects of phrasing and target timing. In Experiment 4, listeners temporally completed (extrapolated) sequences of Experiment 3 that were modified to exclude the target tone. The results again showed that phrase context systematically influenced expectancies about "when" sequences should end. As a set, these studies demonstrate the effects of event structure and anticipatory attending upon experienced duration and are discussed in terms of the expectancy/contrast model.

Adult↗
PubMed1992

Construction and characterization of a mutant of Rhodobacter sphaeroides with the reaction center as the sole pigment-protein complex.

A strain of Rhodobacter sphaeroides has been constructed in which the photosynthetic reaction center is the sole pigment-protein complex. The strain, named RCO1, is capable of photoheterotrophic growth and possesses assembled and functional reaction centers which can undergo photochemical charge separation and are reduced by electrons derived from the cytochrome b/c1 complex. The circular dichroism and linear dichroism of reaction centers in membranes from strain RCO1 are similar to those described previously for reaction centers isolated in detergent solution. A second strain, named RCLH11, which is devoid of the peripheral LH2 antenna complex has also been constructed. A description of the properties of these strains is presented.

Bacteriochlorophylls↗
PubMed1992

Extradural abscess complicating extradural anaesthesia for caesarean section.

Extradural abscess has been described infrequently as a complication of extradural anaesthesia and analgesia. We describe an abscess that developed 5 days after operation in a patient who had extradural anaesthesia for Caesarean section and postoperative analgesia, and review the literature on extradural abscess complicating extradural catheterization, including a discussion on pathogenesis, clinical presentation, diagnosis and management. There have now been 16 reported cases of extradural catheter-related extradural abscess. Only one previous case has been in obstetric practice, despite the widespread use of these techniques in this specialty. A disproportionate number of cases have involved thoracic catheters. Duration of catheterization ranged from 40 h to 6 weeks, the majority of catheters being in place for 5 days or less. The time from catheter placement to development of symptoms ranged from 72 h to 5 months. The causative organism was isolated in 11 cases: Staphylococcus aureus was identified in nine (82%) and Staphylococcus epidermidis in two (18%). Outcome was reported in 15 cases, of which seven (47%) had a full or near full recovery and eight (53%) had a persistent neurological deficit. One case was managed successfully without surgery. Fifty percent of all cases have been reported in the past 5 years. With the increasing use of extradural techniques for anaesthesia and analgesia, this serious complication may be seen more frequently in the future.

Abscess↗
PubMed1992

Mutants of Rhodobacter sphaeroides lacking one or more pigment-protein complexes and complementation with reaction-centre, LH1, and LH2 genes.

The photosynthetic apparatus of Rhodobacter sphaeroides is comprised of three types of pigment-protein complex: the photochemical reaction centre and its attendant LH1 and LH2 light-harvesting complexes. To augment existing deletion/insertion mutants in the genes coding for these complexes we have constructed two further mutants, one of which is a novel double mutant which is devoid of all three types of complex. We have also constructed vectors for the expression of either LH1, LH2 or reaction-centre genes. The resulting system allows each pigment-protein complex to be studied either as part of an intact photosystem or as the sole complex in the cell. In this way we have demonstrated that reaction centres can assemble independently of either light-harvesting complex in R. sphaeroides. In addition, the isolation of derivatives of the deletion/insertion mutants exhibiting spontaneous mutations in carotenoid biosynthesis provides an avenue for examining the role of carotenoids in the assembly of the photosynthetic apparatus. We show that the LH1 complex is assembled regardless of the carotenoid background, and that the type of carotenoid present modifies the absorbance of the LH1 bacteriochlorophylls.

Carotenoids↗