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Biomedical subjects

G Porter

Publications and source records attributed to G Porter.

At least 55 records · Page 3Linked to original sources
PubMed1990

How easy is it to contact the duty medical doctor responsible for acute admissions?

OBJECTIVE: To ascertain ease or difficulty of contacting duty junior doctors responsible for acute medical admissions by telephone. DESIGN: Telephone survey of hospitals in six health regions in England and Wales. SETTING: 70 Randomly selected hospitals, 15 of which were excluded because of non-acceptance of acute medical admissions. PARTICIPANTS: 71 Duty doctors (duty house physicians, senior house officers, or registrars responsible for acute medical admissions) in 48 hospitals; seven duty doctors in seven hospitals were excluded (four declined to participate and three required a written explanation of the survey). 67 Doctors gave full information to all questions. MAIN OUTCOME MEASURES: Time taken for hospital switchboards and duty doctors to reply to telephone call, diagnoses of patients recently admitted, and on call rotas and hours of sleep of duty doctors. RESULTS: Hospital switchboards responded within 30 seconds in 87 (74%) calls, and in 76 calls (64%) the duty doctor requested was contacted within a further two minutes. Chest pain, possibly due to myocardial infarction, was the most common reason for acute medical admissions. Nearly half (48%) of the duty doctors in larger hospitals reported having 4-5 hours sleep or less on their nights on call. Most (30) were on a one in three rota; two were on a one in two rota. CONCLUSIONS: Despite impressions to the contrary contacting the duty medical team by telephone seemed fairly easy. Although most junior doctors were on a rota of one in three or better, insufficient recognition may be given to their deprivation of sleep during nights on duty.

Communication↗
PubMed1990

Comparison of the D1/D2/cytochrome b559 reaction centre complex of photosystem two isolated by two different methods.

Photosystem 2 reaction centre complexes prepared either by solubilisation with Triton X-100 and subsequent exchange into dodecyl maltoside or by a procedure involving a combination of dodecyl maltoside and LiClO4, were characterised in terms of chlorophyll a, pheophytin a, beta-carotene and cytochrome b559 content. Time-resolved chlorophyll fluorescence decay kinetics were measured using both types of complexes. Our data show that the isolated photosystem two reaction centre complex contain, for two pheophytin a molecules, close to six chlorophyll a, two beta-carotene and one cytochrome b559. No major differences were observed in the composition or the kinetic characteristics measured in the samples prepared by the different procedures. Time-resolved fluorescence measurements indicate that more than 94% of the chlorophyll a in both preparations is coupled to the reaction centre complex.

Chlorophyll↗
PubMed1990

U1 small nuclear RNA from Schizosaccharomyces pombe has unique and conserved features and is encoded by an essential single-copy gene.

We have cloned, sequenced, and disrupted the gene encoding U1 small nuclear RNA (snRNA) in the fission yeast Schizosaccharomyces pombe. This RNA is close in size and exhibits a high degree of secondary structure homology to human U1 RNA. There exist two regions of extended primary sequence identity between S. pombe and human U1 RNAs; the first comprises nucleotides involved in hydrogen bonding to 5' splice junctions, and the second is a single-stranded region which, in the human snRNA, forms part of the A protein binding site. S. pombe U1 lacks two nucleotides just following the 5' cap structure which are present in all other U1 homologs examined to date, and the region which corresponds to the binding site for the human 70K protein (molecular weight of 55,000) is more divergent than in other organisms. A putative upstream transcription signal is conserved in sequence and location among all loci encoding spliceosomal snRNAs in S. pombe with the exception of U6. Disruption of the single-copy U1 gene, designated snu1, reveals that this RNA is indispensable for viability.

Base Sequence↗
PubMed1988

U2 small nuclear RNA is remarkably conserved between Schizosaccharomyces pombe and mammals.

We report the molecular cloning and sequencing of the most abundant trimethylguanosine-capped small nuclear RNA from the fission yeast Schizosaccharomyces pombe, a highly conserved homolog of mammalian U2 small nuclear RNA. This RNA is 186 nucleotides in length, just 2 nucleotides shorter than its human counterpart; this is in contrast to Saccharomyces cerevisiae U2, which is 1,175 nucleotides long. Moreover, the secondary structure of Schizosaccharomyces pombe U2 is virtually identical to that of mammalian U2, including the 3' half of the RNA, which shows limited primary sequence identity. Northern (RNA) blot analysis revealed that the size of this RNA is conserved not only in fission yeasts but in many organisms, including other ascomycetes.

Animals↗
PubMed1988

Identification of an essential Schizosaccharomyces pombe RNA homologous to the 7SL component of signal recognition particle.

We have cloned the gene encoding a novel small cytoplasmic RNA from the fission yeast Schizosaccharomyces pombe. Four lines of evidence support the idea that this RNA is a homolog of the 7SL RNA component of mammalian signal recognition particle (SRP), which targets presecretory proteins to the endoplasmic reticulum membrane. First, it shares limited but significant primary sequence homology with previously identified 7SL RNAs and can be folded into a similar secondary structure. Second, it possesses the 5' triphosphate characteristic of unprocessed RNA polymerase III transcripts, and moreover, it is the only fission yeast RNA in this size range with such a terminus. Third, its behavior in cell fractionation experiments suggests that it is part of a small ribonucleoprotein which forms salt-labile contacts with larger structures. Fourth, the particle containing S. pombe 7SL RNA resembles mammalian SRP in both size (11S) and affinity for DEAE-Sepharose. Disruption of the single-copy gene, designated slr1+, reveals that the RNA is indispensable for growth in fission yeast. This result is not surprising, since secretion is an essential cellular process.

Base Sequence↗
PubMed1985

Triage success in disasters: dynamic victim-tracking cards.

A dynamic victim-tracking card developed for use in community or hospital disaster exercises was tested during two hospital and two airport disaster drills. Use of the card in 375 "patients" allowed testing of the ability to evaluate the decisions of triage, the early medical intervention for "victims," and the ongoing treatment of patients with a changing medical status. The card was successful in simulating realistic changes that may occur in critically ill and injured patients. Of the 126 "patients" evaluated in an actual exercise, 55 (43.6%) were placed in the proper triage category. Four patients "died" as a result of poor initial evaluation and treatment. Medical decisions during hospital and community disaster exercises can be more realistically tested and more accurately documented with the use of the dynamic victim-tracking card.

Abdominal Injuries↗
PubMed1984

Picosecond spectroscopy: applications in biochemistry. Part I: Techniques.

A number of sources of picosecond optical pulses and the means by which they may be used to investigate fast molecular processes have been described. In addition, it should be pointed out that most of these techniques can be extended to take advantage of other properties of the laser pulses; in particular, the polarization is of use in measuring time-dependent antisotropy. The state of the art is now the generation of 30fs pulses; it seems likely that this is all the time resolution that one is likely to need for investigating biological and other molecular processes as at such short times the uncertainty principle leads to a considerable loss of spectral resolution.

Argon↗
PubMed1979

Picosecond time-resolved fluorescence study of chlorophyll organisation and excitation energy distribution in chloroplasts from wild-type barley and a mutant lacking chlorophyll b.

Picosecond time-resolved fluorescence spectroscopy has been used to investigate the fluorescence emission from wild-type barley chloroplasts and from chloroplasts of the barley mutant, chlorina f-2, which lacks the light-harvesting chlorophyll a/b-protein complex. Cation-controlled regulation of the distribution of excitation energy was studied in isolated chloroplasts at the Fo and Fm levels. It was found that: (a) The fluorescence decay curves were distinctly non-exponential, even at low excitation intensities (less than 2 x 10(14) photons . cm(-2). (b) The fluorescence decay curves could, however, be described by a dual exponential decay law. The wild-type barley chloroplasts gave a short-lived fluorescence component of approximately 140 ps and a long-lived component of 600 ps (Fo) or 1300 ps (Fm) in the presence of Mg2+; in comparison, the mutant barley yielded a short-lived fluorescence component of approx. 50 ps and a long-lived component of 194 ps (Fo) and 424 ps (Fm). (c) The absence of the light-harvesting chlorophyll a/b-protein complex in the mutant results in a low fluorescence quantum yield which is unaffected by the cation composition of the medium. (d) The fluorescence yield changes seen in steady-state experiments on closing Photosystem II reaction centres (Fm/Fo) or on the addition of MgCl2 (+Mg2+/-Mg2+) were in overall agreement with those calculated from the time-resolved fluorescence measurements. The results suggest that the short-lived fluorescence component is partly attributable to the chlorophyll a antenna of Photosystem I, and, in part, to those light-harvesting-Photosystem II pigment combinations which are strongly coupled to the Photosystem I antenna chlorophyll. The long-lived fluorescence component can be ascribed to the light-harvesting-Photosystem II pigment combinations not coupled with the antenna of Photosystem I. In the case of the mutant, the two components appear to be the separate emissions from the Photosystem I and Photosystem II antenna chlorophylls.

Chlorophyll↗
PubMed1979

The fluorescence decay kinetics of in vivo chlorophyll measured using low intensity excitation.

We report fluorescence lifetimes for in vivo chlorophyll a using a time-correlated single-photon counting technique with tunable dye laser excitation. The fluorescence decay of dark-adapted chlorella is almost exponential with a lifetime of 490 ps, which is independent of excitation from 570 nm to 640 nm. Chloroplasts show a two-component decay of 410 ps and approximately 1.4 ns, the proportion of long component depending upon the fluorescence state of the chloroplasts. The fluorescence lifetime of Photosystem I was determined to be 110 ps from measurements on fragments enriched in Photosystem I prepared from chloroplasts with digitonin.

Chlorella↗
PubMed1979

Reduced T cell reactivity in vasectomized rhesus monkeys: association with histocompatibility type.

The capacity of peripheral lymphocytes from rhesus monkeys which had been vasectomized for 7 or 11 years to stimulate and respond to normal rhesus lymphocytes in mixed lymphocyte cultures (MLC) was tested to determine whether vasectomy affects immunologic reactivity. The ability to respond in MLC, a T cell function, was significantly reduced in the 11-year vasectomized animals and in two 7-year vasectomized animals. The ability to stimulate in MLC, a B cell function, was significantly increased in the 11-year vasectomized group. MLC reactivity of normal lymphocytes cultured in plasma from vasectomized animals and lymphocytes from vasectomized animals cultured in normal plasma was not altered, ruling out serum effects in the reduction of MLC responsiveness in these vasectomized animals. Seventy-five per cent of the vasectomized animals with markedly reduced MLC reactivity had the RhL-A determinates 19 and 24, indicating an association between the tendency toward reduced MLC reactivity after vasectomy and histocompatibility type.

Animals↗
PubMed1978

Picosecond time-resolved energy transfer in Porphyridium cruentum. Part I. In the intact alga.

The wavelength-resolved fluorescence emission kinetics of the accessory pigments and chlorophyll a in Porphyridium cruentum have been studied by pico-second laser spectroscopy. Direct excitation of the pigment B-phycoerythrin with a 530 nm, 6 ps pulse produced fluorescence emission from all of the pigments as a result of energy transfer between the pigments to the reaction centre of Photosystem II. The emission from B-phycoerythrin at 576 nm follows a nonexponential decay law with a mean fluorescence lifetime of 70 ps, whereas the fluorescence from R-phycocyanin (640 nm), allophycocyanin (660 nm) and chlorophyll a (685 nm) all appeared to follow an exponential decay law with lifetimes of 90 ps, 118 ps and 175 ps respectively. Upon closure of the Photosystem II reaction centres with 3-(3,4-dichlorophenyl)-1,1-dimethylurea and preillumination the chlorophyll a decay became non-exponential, having a long component with an apparent lifetime of 840 ps. The fluorescence from the latter three pigments all showed finite risetimes to the maximum emission intensity of 12 ps for R-phycocyanin, 24 ps for allophycocyanin and 50 ps for chlorophyll a. A kinetic analysis of these results indicates that energy transfer between the pigments is at least 99% efficient and is governed by an exp --At1/2 transfer function. The apparent exponential behaviour of the fluorescence decay functions of the latter three pigments is shown to be a direct result of the energy transfer kinetics, as are the observed risetimes in the fluorescence emissions.

Chlorophyll↗
PubMed1978

Picosecond time-resolved energy transfer in Porphyridium cruentum. Part II. In the isolated light harvesting complex (phycobilisomes).

The transfer of excitation energy between phycobiliproteins in isolated phycobilisomes has been observed on a picosecond time scale. The photon density of the excitation pulse has been carefully varied so as to control the level of exciton interactions induced in the pigment bed. The 530 nm light pulse is absorbed predominantly by B-phycoerythrin, and the fluorescence of this component rises within the pulse duration and shows a mean 1/e decay time of 70 ps. The main emission band, centred at 672 nm, is due to allophycocyanin and is prominent because of the absence of energy transfer to chlorophyll. Energy transfer to this pigment from B-phycoerythrin via R-phycocyanin produces a risetime of 120 ps to the fluorescence maximum. The lifetime of the allophycocyanin fluorescence is found to be about 4 ns using excitation pulses of low photon densities (10(13) photons.cm-2), but decreases to about 2 ns at higher photon densities. The relative quantum yield of the allophycocyanin fluorescence decreases almost 10 fold over the range of laser pulse intensities, 10(13)--10(16) photons-cm-2. Fluorescence quenching by exciton-exciton annihilation is only observed in allophycocyanin and could be a consequence of the long lifetime of the single exciton in this pigment.

Energy Transfer↗