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Biomedical subjects

M R Jones

Publications and source records attributed to M R Jones.

At least 55 records · Page 3Linked to original sources
PubMed1999

Reorientation of the acetyl group of the photoactive bacteriopheophytin in reaction centers of Rhodobacter sphaeroides: an ENDOR/TRIPLE resonance study.

The freeze-trapped bacteriopheophytin alpha radical anion phi(*)A- has been investigated by 1H-ENDOR/Special TRIPLE resonance spectroscopy in photosynthetic reaction centers of Rhodobacter sphaeroides, in which the Tyr at position M210 had been replaced by either Phe, Leu, His or Trp. In the wild type reaction center and the mutants YF(M210) and YW(M210) two distinct states of phi(*)A-, denoted I(*)1- and I(*)2-, can be stabilized below 200 K. The state I(*)1 is metastable and relaxes to I(*)2- as the temperature is raised from 135 K to 180 K. The difference in the electronic structure of phi(*)A- between the two states is interpreted in terms of a conformational change of phiA after freeze-trapping, involving a reorientation of the 3-acetyl group with respect to the macrocycle of the bacteriopheophytin. This interpretation is supported by the results of RHF-INDO/SP calculations. In the YH(M210) reaction center only one phiA- state is obtained that is distinct from I(*)1- and I(*)2, and the observed electronic structure indicates an almost in-plane orientation of the 3-acetyl group. This is consistent with the proposal that a hydrogen bond is formed between His M210 and the 3(1)-keto oxygen of phiA that impedes the reorientation of the acetyl group. Only one phi(*)A- state is observed in the YL(M210) reaction center, which is similar to the metastable state I(*)1 in the wild type complex. This result is interpreted in terms of a steric hindrance of the reorientation of the 3-acetyl group that is exerted by the side chain of Leu at position M210. Possible implications of these findings for the mechanism of electron transfer in bacterial reaction centers are discussed.

Electron Spin Resonance Spectroscopy↗
PubMed1999

Cerebral polyopia with extrastriate quadrantanopia: report of a case with magnetic resonance documentation of V2/V3 cortical infarction.

This is a case report of the occurrence of cerebral diplopia with right-side superior homonymous quadrantanopia in a young woman after chiropractic neck manipulation. Magnetic resonance imaging confirmed an infarct in the left inferior V2/V3 (extrastriate) cortex. The characteristics of the diplopia are illustrated with the patient's drawings, and persisting abnormalities in perception are described in the area of the initial field defect after static (computed) visual field testing yielded normal results.

Adult↗
PubMed1998

Low frequency vibrational modes in proteins: changes induced by point-mutations in the protein-cofactor matrix of bacterial reaction centers.

As a step toward understanding their functional role, the low frequency vibrational motions (<300 cm-1) that are coupled to optical excitation of the primary donor bacteriochlorophyll cofactors in the reaction center from Rhodobacter sphaeroides were investigated. The pattern of hydrogen-bonding interaction between these bacteriochlorophylls and the surrounding protein was altered in several ways by mutation of single amino acids. The spectrum of low frequency vibrational modes identified by femtosecond coherence spectroscopy varied strongly between the different reaction center complexes, including between different mutants where the pattern of hydrogen bonds was the same. It is argued that these variations are primarily due to changes in the nature of the individual modes, rather than to changes in the charge distribution in the electronic states involved in the optical excitation. Pronounced effects of point mutations on the low frequency vibrational modes active in a protein-cofactor system have not been reported previously. The changes in frequency observed indicate a strong involvement of the protein in these nuclear motions and demonstrate that the protein matrix can increase or decrease the fluctuations of the cofactor along specific directions.

Bacterial Proteins↗
PubMed1998

The LH1-RC core complex of Rhodobacter sphaeroides: interaction between components, time-dependent assembly, and topology of the PufX protein.

Mutant strains of the photosynthetic bacterium Rhodobacter sphaeroides, lacking either LH1, the RC or PufX, were analysed by mild detergent fractionation of the cores. This reveals a hierarchy of binding of PufX in the order RC:LH1 > LH1 > RC. The assembly of photosynthetic membranes was studied by switching highly aerated cells to conditions of low aeration in the dark. The RC-H subunit appears before other components, followed by the pufBALMX then pufBA transcripts. Synthesis of the PufX polypeptide precedes that of LH1alpha and beta, which suggests that PufX associates with a limited amount of LH1alpha, beta and the RC, and prior to the encirclement of the RC by the rest of the LH1 complex. The topology of PufX within the intracytoplasmic membrane was determined by proteolytic treatment of membrane vesicles followed by protein sequencing; PufX is N-terminally exposed on the cytoplasmic surface of the photosynthetic membrane.

Amino Acid Sequence↗
PubMed1998

Structural studies of wild-type and mutant reaction centers from an antenna-deficient strain of Rhodobacter sphaeroides: monitoring the optical properties of the complex from bacterial cell to crystal.

Reaction centers have been crystallized from the antenna-deficient RCO2 strain of Rhodobacter sphaeroides, and a structural model has been constructed at 2.6 A resolution. The antenna-deficient strain allows assessment of the structural integrity of the reaction center at each stage in the purification-crystallization procedure. Spectroscopic evidence indicates that the properties of the reaction center bacteriopheophytins and the primary donor bacteriochlorophylls are modified somewhat on removal of the protein complex from the membrane and that these changes are carried through to the crystal form of the reaction center. The structure of a FM197R/YM177F mutant reaction center has also been determined to 2.55 A resolution. The mutant complex shows an unexpected change in structure, with a significant reorientation of the new arginine, the incorporation of a new water molecule into the structure, and rotation of the 2-acetyl carbonyl group of one of the primary donor bacteriochlorophylls to a more out-of-plane geometry. Changes in the optical spectrum of the FM197R/YM177F reaction center are discussed with respect to the altered structure of the complex.

Crystallography, X-Ray↗
PubMed1998

Hospital-acquired blood stream infections in New Zealand.

AIM: To determine the number and rates of hospital-acquired blood stream infections in New Zealand public hospitals. METHOD: From October 1994 to December 1996 each of the 23 Crown Health Enterprises (CHEs) provided the Crown Company Monitoring Advisory Unit with data on the number of episodes of hospital-acquired blood stream infection (HA-BSI) and the number of inpatient admissions. RESULTS: During the 27 month study period, 3049 episodes of HA-BSI occurred in an inpatient population of 1 300 892 giving a national average rate of 0.23%. HA-BSI rates were highest for the six tertiary level, metropolitan CHEs (range 0.19% - 0.56%) in which 79% of all HA-BSIs occurred. CONCLUSION: The HA-BSI rate for New Zealand is within the range that would be expected for a developed country with a comprehensive health service. The variability between CHEs in terms of the clinical services provided and case mix differences invalidates direct comparison of HA-BSI rates. Surveillance for HA-BSI should continue with the collection of data which would allow meaningful comparison of similar tertiary level services.

Bacteremia↗
PubMed1998

Tetrodotoxin: anesthetic activity in the de-epithelialized cornea.

BACKGROUND: Tetrodotoxin (TTX) binds with high affinity to sodium channels and produces local anesthesia. We investigated whether TTX is an effective, long-acting corneal anesthetic in rabbits. METHODS: After mechanical debridement of the central corneal epithelium, topical TTX (1 mM, 0.1 mM, or 0.01 mM) was applied to one eye each of 18 New Zealand White rabbits. The fellow eye of each rabbit was treated with control vehicle. Blink response to a mechanical stimulus was assessed. Blink response was also assessed every 3 h for 30 h in 6 rabbits treated with 1 mM TTX administered every 6 h. In a separate group of 12 rabbits with central epithelial debridement, the rate of epithelial healing was compared between animals treated with topical 1.0 mM TTX and animals receiving no treatment. RESULTS: After 4 h, eyes treated with 1.0 mM and 0.1 mM TTX were anesthetic. At 6 h, five of six rabbit eyes treated with 1.0 mM TTX were still partially anesthetic. By 8 h, the mean anesthesia score for 1.0 mM TTX was approaching normal. With multiple dosing, all six rabbit eyes remained anesthetic for the duration of the experiment. There was no significant difference in the rate of re-epithelialization between eyes treated with TTX and untreated controls. There was no evidence of systemic or local toxicity from topical TTX. CONCLUSION: In a rabbit model, TTX is a long-acting topical anesthetic that retains its effectiveness when administered repeatedly over 24 h and does not inhibit epithelial healing. It may have application in management of pain after photorefractive keratectomy.

Administration, Topical↗
PubMed1998

Cystoid macular edema associated with cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome.

PURPOSE: To describe the clinical and fluorescein angiographic appearance of cystoid macular edema associated with cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome (AIDS). METHODS: We retrospectively examined the clinical and photographic records of four patients with AIDS and cytomegalovirus retinitis who developed cystoid macular edema. RESULTS: Seven eyes of four patients with AIDS and cytomegalovirus retinitis experienced decreased vision associated with cystoid macular edema. Vitreous inflammation was mild in each patient. In all eyes, the retinitis involved zone 1, and in all but one eye, the cytomegalovirus retinitis was inactive. In one eye, the cystoid macular edema was worsened by formation of a dense juxtafoveal epiretinal membrane. CONCLUSIONS: Although infrequently recognized, cystoid macular edema can cause visual loss in patients with AIDS and cytomegalovirus retinitis. Fluorescein angiography should be considered in any patient with cytomegalovirus retinitis and unexplained visual loss.

AIDS-Related Opportunistic Infections↗
PubMed1998

Experimental study of tetrodotoxin, a long-acting topical anesthetic.

PURPOSE: To determine the effectiveness and toxicity of tetrodotoxin for use as a long-acting topical anesthetic. METHODS: Four groups of six rabbits each received a 40-microl aliquot of either tetrodotoxin in one of three concentrations (10 mM, 1 mM, or 0.1 mM) or proparacaine 0.5% into the inferior conjunctival cul-de-sac of one eye, with the fellow eye of each rabbit receiving 40 microl of a 60-mM, pH 4.3 sodium citrate vehicle as a control. Corneal sensation was tested for up to 8 hours after administration of drugs, and response was noted by no blink, partial blink without full eyelid closure, and full blink. Slit-lamp examination at 12 and 24 hours after administration and pachymetry before and 24 hours after administration were performed to detect corneal toxicity. RESULTS: Rabbits receiving all three concentrations of tetrodotoxin did not demonstrate any ocular irritation, corneal thickening, or signs of systemic toxicity. At a dose of 10 mM, tetrodotoxin produced an anesthetic effect lasting up to 8 hours. At 1 mM, tetrodotoxin was an effective but shorter-acting anesthetic. At 0.1 mM, tetrodotoxin had no significant anesthetic effect. Proparacaine-treated rabbits initially were anesthetic, but this effect was largely gone by 1 hour and completely gone by 3 hours. CONCLUSIONS: Tetrodotoxin is a long-acting topical anesthetic in the rabbit cornea. Although additional toxicity studies are required, tetrodotoxin may provide an effective, long-lasting topical anesthetic for use in pain control after corneal procedures such as photorefractive keratectomy.

Anesthesia, Local↗
PubMed1998

Essential carbamoyl-amino acids formed in vivo in patients with end-stage renal disease managed by continuous ambulatory peritoneal dialysis: isolation, identification, and quantitation.

Carbamoyl-amino acids (C-AA) are formed by reaction of amino acids with cyanate, which is spontaneously formed from urea at body temperature and pH. In vivo derivatized C-AA are not measured by the usual amino acid analysis methods, which require a free amino group for derivatization. Free-amino acids (F-AA) but no C-AA were found in the postabsorptive plasma of eight normal persons with blood urea nitrogen (BUN) levels ranging from 9 to 16 mg/dl. In a longitudinal study of postprandial plasma (n=43), essential amino acids, both C-AA and F-AA, were isolated and quantified by reverse-phase high-pressure liquid chromatography in six patients with end-stage renal disease who were managed by continuous ambulatory peritoneal dialysis. The mean BUN was 61 mg/dl (range, 36 to 79 mg/dl). In uremia, removal of F-AA from the essential amino acid pool to form C-AA is measured by the ratio of C-AA to F-AA (carbamoylation index (CI)). Using the mean value for each essential amino acid, the CIs were as follows: leucine, 4; valine, 3.3; isoleucine, 11.4; threonine, 9; lysine, 2; methionine, 3.5; histidine, 3.5; phenylalanine, 0.5; and tyrosine, 1.3. Carbamoylation of F-AA may account, in part, for the lower than normal levels of F-AA in patients with uremia. The derivatized amino group of C-AA interferes with formation of a peptide bond in protein synthesis, which requires an underivatized amino acid. A decrease in the F-AA pool available for protein synthesis and anabolism in the presence of C-AA may provide additional contributing factors for the development of malnutrition in uremia.

Adult↗
PubMed1998

Demonstration of the key role played by the PufX protein in the functional and structural organization of native and hybrid bacterial photosynthetic core complexes.

The role of a component of the bacterial photosystem, the PufX protein, was examined by heterologous expression of the pufX gene from Rhodobacter capsulatus in a strain of R. sphaeroides that lacks the native pufX gene. The strain of R. sphaeroides containing the R. capsulatus PufX protein was capable of efficient transduction of light energy despite a low degree of sequence conservation between the PufX proteins from the two species. The organization of the hybrid reaction center/LH1 photosystem in strains of R. sphaeroides containing the R. capsulatus LH1 antenna complex was affected differently by the R. sphaeroides and R. capsulatus PufX proteins. We discuss the implications of our findings for the role of the PufX protein in organizing the bacterial photosystem for efficient transduction of light energy.

Amino Acid Sequence↗
PubMed1998

Ultrasound assisted lipoplasty--Part 1: An overview for nurses.

The use of ultrasound assisted lipoplasty (UAL) to assist in the removal of subcutaneous fat has been practiced in Europe for nearly a decade but has only recently been practiced in the United States. This article will discuss the UAL procedure, its history, regulatory issues, instrumentation and equipment needed, clinical protocol, case reports, complications, and future considerations.

Education, Nursing, Continuing↗
PubMed1997

Primary electron transfer kinetics in membrane-bound Rhodobacter sphaeroides reaction centers: a global and target analysis.

Absorbance difference kinetics were measured on quinone-reduced membrane-bound wild type Rhodobacter sphaeroides reaction centers in the wavelength region from 690 to 1060 nm using 800 nm excitation. Global analysis of the data revealed five lifetimes of 0.18, 1.9, 5.1, and 22 ps and a long-lived component for the processes that underlie the spectral evolution of the system. The 0.18 ps component was ascribed to energy transfer from the excited state of the accessory bacteriochlorophyll (B*) to the primary donor (P*). The 1.9 ps component was associated with a state involving a BChl anion absorbing in the 1020 nm region. This led to the conclusion that primary electron transfer is best described by a model in which the electron is passed from P* to the acceptor bacteriopheophytin (HL) via the monomeric bacteriochlorophyll (BL), with the formation of the radical pair state . An analysis assuming partial direct charge separation from B* [Van Brederode, M. E., Jones, M. R., and Van Grondelle, R. (1997) Chem. Phys. Lett. 268, 143-149] was also consistent with the data. Within the framework of a five component model, the 5.1 and 22 ps lifetimes were associated with charge separation and relaxation of the radical pair state respectively, providing a description which adequately accounted for the complex kinetics of decay of P*. Alternatively, by assuming that the 5.1 and 22 ps components originate from a single component with a multi-exponential decay, a simpler analysis with only four components could be employed, resulting in only a small increase (7%) in the weighted root mean square error of the fit. In both descriptions part of the decay of P* proceeds with a lifetime of about 2 ps. The relative merits of these alternative descriptions of the primary events in light-driven electron transfer are discussed. Similar measurements on YM210H mutant reaction centers revealed four lifetimes of 0.2, 3.1, and 12 ps and a long-lived component. The 3.1 and 12 ps lifetimes are ascribed to multi-exponential decay of the P* state. The differences with the WT data are discussed.

Electron Transport↗