Biomedical subjects
Publications and source records attributed to M R Jones.
New crystallographic data for the bacterial photoreaction centre have brought an intriguing insight into the structural changes that accompany the primary event in photosynthesis, the conversion of light energy into chemical energy.
It is generally accepted that electron transfer in bacterial photosynthesis is driven by the first singlet excited state of a special pair of bacteriochlorophylls (P*). We have examined the first steps of electron transfer in a mutant of the Rhodobacter sphaeroides reaction center in which charge separation from P* is dramatically slowed down. The results provide for the first time clear evidence that excitation of the monomeric bacteriochlorophyll in the active branch of the reaction center (B(A)) drives ultrafast transmembrane electron transfer without the involvement of P*, demonstrating a new and efficient mechanism for solar energy transduction in photosynthesis. The most abundant charge-separated intermediate state probably is P+B(A)-, which is formed within 200 fs from B(A)* and decays with a lifetime of 6.5 ps into P+H(A)-. We also see evidence for the involvement of a B(A)+H(A)- state in the alternative pathway.
AIMS: To determine the current susceptibility pattern of bacterial isolates from intensive care and haematology/oncology patients in New Zealand. METHOD: Over a 6 month period 417 consecutive clinically relevant bacterial isolates from intensive care and haematology/oncology patients from seven New Zealand hospitals had their susceptibility to multiple antimicrobial agents determined by the agar plate dilution method. Methicillin resistant staphylococci were not included. RESULTS: Of the 417 isolates, 224 (54%) were gram negative and 193 were gram positive. Predominant species/groups were: Escherichia coli 63 (15%), Enterobacter spp 26 (6%), other Enterobacteriacae 41 (10%), Pseudomonas aeruginosa 42 (10%), Staphylococcus aureus 111 (27%), coagulase negative staphylococci 30 (7%), Streptococcus spp 31 (7%), and Enterococcus spp 19 (5%). Isolate sources were: respiratory tract, 170 (41%); cutaneous sites, 81 (19%); blood, 64 (15%); and urine 63 (15%). Resistance was uncommon amongst staphylococci, streptococci, enterococci, and H influenzae. No vancomycin resistant or beta-lactamase-positive enterococci were encountered. For different groups of enteric gram negative bacilli: amoxycillin and amoxycillin-clavulanic acid resistance was common, 46-93% and 24-85% respectively; cefpirome was the most active cephalosporin; aminoglycoside resistance was uncommon; and no isolate possessed extended spectrum beta-lactamase. For P aeruginosa: most isolates were susceptible to cefpirome and ceftazidime, and aminoglycoside resistance was uncommon. CONCLUSION: Gram positive bacteria make up a higher proportion of isolates than in a similar European study. At present New Zealand does not have widespread resistance amongst common isolates. Several agents currently available in New Zealand provide adequate cover for commonly encountered pathogens. The choice of which agent to choose therefore rests more with their purchase and administration costs, as well as safety and efficacy data than simply susceptibility data alone.
Explore the source record for details and available documents.
Images of a tissue simulating phantom are obtained by inverting a limited number of continuous-wave relative transmission measurements. The diffusion approximation to the radiative transfer equation is used as a light propagation model. The inversion procedure is based on a quasi-Newton method and the Levenberg-Marquardt method, and the imaging parameter is the absorption coefficient of the phantom. It is shown that the resolution of the images can be improved using the zooming method. The image indicates the presence of an inhomogeneity in approximately the correct location, but the shape and size of the inhomogeneity in the reconstructed image differs from the shape and size of the actual inhomogeneity. Possible methods for further enhancement of the images are discussed.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Femtosecond spectroscopy was used to study vibrational dynamics in the first singlet excited state (P*) of the primary donor of bacterial reaction centers (RC)in which primary electron transfer dynamics have been altered by single amino acid modifications. We studied intracytoplasmic RC-only membranes containing Rhodobacter sphaeroides wild-type RCs and RCs bearing mutations in the vicinity of P, where Tyr M210 was modified to His, Leu, and Trp and where Phe L181 was modified to Tyr. These mutations do not change the frequencies of the main low-frequency activated modes, which is consistent with a description in which these modes involve extended regions of the protein. Electron transfer in FL181Y, YM210H, and wild-type RCs at 10 K occurs in approximately 1 ps or less, and damping of the coherences occurs simultaneously with the decay of the P* excited state. These results, and a comparison with YM210L RCs, show that in wild-type RCs the damping is primarily determined by the depletion of P* and not by vibrational dephasing induced by interactions with the bath or nonharmonic coupling. In the YM210L and W mutants, electron transfer occurs on a time scale of hundreds of picoseconds at 10 K. Analysis of the longer-lasting vibrational dynamics in these mutants sets a new lower limit for the intrinsic vibrational dephasing time of 1.2 ps for some modes, but of approximately 2 ps for most activated modes.
The light harvesting antenna 1 (LH1) complex of Rhodobacter sphaeroides is intimately associated with the reaction center (RC) as part of the reaction center RC-LH1 core complex. The pufA gene has been modified such that between 5 and 16 amino acid residues were progressively deleted from the C terminus of the LH1 alpha polypeptide. The two largest deletions produced strains which were deficient in LH1. The remaining four deletion mutants exhibited significant reductions in the average level of LH1 per reaction center. Analysis of detergent-solubilized cores on sucrose gradients showed that the mutant strains had a sizeable population of antenna-deficient reaction centers in addition to core complexes with a reduced ratio of LH1:RC. The decrease in the ratio of LH1:RC in core complexes of the mutant strains was accompanied by a progressive blue shift of the absorbance maximum of LH1, which we attribute to the reduced aggregation state of LH1 in the smaller cores. The PufX polypeptide was not required for photosynthetic growth in mutants with reduced core sizes. We conclude that the level of LH1 in the bacterial membrane, and the aggregation state of LH1 in core complexes, are both influenced by the C terminus of the alpha polypeptide, and we discuss possible models for the organization of the core complex in Rb. sphaeroides.
In a target detection task involving sustained attentional monitoring, rhythmic properties of tone sequences were found to affect detection performance (area under receiver-operating characteristic curves) and reaction times. Alternating tone frequencies (high, low) formed three different recurrent rhythms (binary, trinary, mixed) which varied in complexity. Attentional set was also manipulated so that participants attended either to tones of both frequencies (divided) or to only the higher of the two tones (selective). The most interesting finding involved an interaction between attention set and rhythm, indicating that selective attending is enhanced by the most complex (mixed) rhythm, whereas divided attending tends to be best with the simplest rhythm (binary). Results are discussed in terms of a theory of dynamic attending, in which it is assumed that listeners actively use attending oscillators to direct attending.
We report studies of energy transfer from the 800-nm absorbing pigment (B800) to the 850-nm absorbing pigment (B850) of the LH2 peripheral antenna complex and from LH2 to the core antenna complex (LH1) in Rhodobacter (Rb.) sphaeroides. The B800 to B850 process was studied in membranes from a LH2-reaction center (no LH1) mutant of Rb. sphaeroides and the LH2 to LH1 transfer was studied in both the wild-type species and in LH2 mutants with blue-shifted B850. The measurements were performed by using approximately 100-fs pulses to probe the formation of acceptor excitations in a two-color pump-probe measurement. Our experiments reveal a B800 to B850 transfer time of approximately 0.7 ps at 296 K and energy transfer from LH2 to LH1 is characterized by a time constant of approximately 3 ps at 296 K and approximately 5 ps at 77 K. In the blue-shifted B850 mutants, the transfer time from B850 to LH1 becomes gradually longer with increasing blue-shift of the B850 band as a result of the decreasing spectral overlap between the antennae. The results have been used to produce a model for the association between the ring-like structures that are characteristic of both the LH2 and LH1 antennae.
Explore the source record for details and available documents.
Quantification of the dialysis dose and assessment of nutritional status and response to nutritional therapy have become standard parts of the management of the chronic dialysis patient. Although advances in these areas have led to a more rational basis for therapy, certain misconceptions and points of confusion appear to have occurred. Recognizing the importance of a standard nomenclature to the development of concepts and the communication of research findings, we have attempted to compile a list of terms that are commonly used in the field of dialysis. New terms have been proposed for current ones that do not seem adequate. In addition, we have discussed potential methodologies for obtaining more accurate data for dialysis kinetics and for precise monitoring of nutritional intake and status. It is hoped that this glossary will stimulate discussion that will lead to refinements in terminology and concepts that will, in turn, improve research and practice in nephrology. It is anticipated that many of these definitions and recommendations will be modified or superseded as the management of patients with renal failure continues to advance.
Four experiments examined attentional flexibility in listening to polyrhythmic patterns. Musically trained and untrained listeners detected changes in timing of 1 tone (the lower tone) in a 3:2 polyrhythm in which high and low tones varied in frequency separation. Experiment 1 encouraged integrative attending; all listeners performed significantly poorer in conditions with wide as opposed to narrow frequency separations. Experiment 2, which encouraged selective attending to low tones, reversed these results: Performance was poorer in the narrow frequency conditions. In neither experiment did skill interact with frequency separation. Experiments 3 and 4 extended these findings to moderate frequency separations. Over all experiments, musically trained listeners exhibited an enhanced ability to detect timing variations, but not flexibility of perceptual organization as it applies to detection of timing changes. Instead, pattern structure (e.g., frequency and time relation) decisively influenced perception for both levels of skill.
Two experiments investigated the influence of melodic and harmonic context on the obviousness of pitch changes in 3 Western tonal melodies. In Experiment 1, listeners with different levels of musical skill heard standard melodies followed by comparison melodies in which single pitch changes could occur. In-key pitch changes that were not implied by the local harmony were judged more obvious than in-key pitch changes that were so implied. This effect was influenced by the surrounding context of melodic line and chords and was absent when the context contained chords that were not consistent with the harmony implied by the melodic line. In Experiment 2, with similar listeners, implied harmony effects were eliminated by removing parts of the melodic line, indicating the relative importance of melodic context as a determinant of implied harmony. Questionnaire data suggested that knowledge of tonal relationships was tacit, even in many trained listeners.
With the advent of continuous quality improvement and the '90s focus on patient or customer satisfaction, hospitals have started to try to identify what their patients or customers want. Hospitals serve communities of one sort or another, whether local communities or statewide communities for highly specialized procedures. They need to consult at least their local communities as part of a quality improvement process and also to help determine future directions. Austin Hospital in Australia decided to establish a formal advisory committee in order to accomplish this consultation. Although there have been minor deficiencies in the arrangement, the advisory committee has largely fulfilled the promise for which it was created more than seven years ago.
Explore the source record for details and available documents.
In regard to the question posed in the title of this review, the answer is mixed. IPN is possible today but only on a limited basis and at high cost with uncertain benefit. A 1.1% amino acid dialysis solution for IPAA therapy is available in several European countries but has not yet been approved for use in the United States. When it becomes more widely available, IPAA should become an important tool, along with other types of therapy, for use in the maintenance of good nutritional status in PD patients.