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Biomedical subjects

T Mar

Publications and source records attributed to T Mar.

18 recordsLinked to original sources
PubMed1995

Origin of optical activity in the purple bacterial photoreaction center.

The photoreaction center (RC) of purple bacteria contains four bacteriochlorophyll (Bch) and two bacteriopheophytin (Bph) molecules as prosthetic groups. Their optical activity, as measured by circular dichroism (CD) spectroscopy, is largely increased in situ as compared to organic solutions. The all-exciton hypothesis posits that this enhanced optical activity is entirely due to excitonic interactions between the electronic transitions of all six bacteriochlorin molecules. Using the simple exciton theory, this model predicts that the near-infrared CD spectra should be conservative. The fact that they are not, whether the special pair of Bch (SP) that constitutes the primary electron donor is reduced or oxidized, has been explained by hyperchromic effects. The present work tests this hypothesis by successively eliminating the absorption and, therefore, the optical activity of the Bphs and of the non-special-pair (non-SP) Bchs. This was accomplished by trapping these pigments in their reduced state. RC preparations with the four non-SP bacteriochlorins trapped in their reduced state and, therefore, with an intact SP displayed conservative CD spectra. RC preparations with only the electronic transitions of SP and of one non-SP Bch also showed conservative CD spectra. These conservative CD spectra and their corresponding absorption spectra were simulated using simple exciton theory without assuming hyperchromic effects. Bleaching half of the 755-nm absorption band by phototrapping one of the two Bph molecules led to the complete disappearnce of the corresponding CD band. This cannot be explained by the all-exciton hypothesis. These results suggest that the optical activity of the SP alone, or with one non-SP Bch, is due to excitonic interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Ascorbic Acid↗
PubMed1994

An aggressive surgical approach to the management of chronic osteomyelitis.

This is a review of 13 patients with chronic osteomyelitis treated at the author's institution using techniques similar to the management of giant cell tumors of bone. This included aggressive serial debridements and appropriate antibiotic coverage and subsequent bone-grafting or soft-tissue coverage procedures. The number of surgical procedures ranged from three to eight (average 4.2) and were performed every two to three days. Empiric antibiotics were started after cultures were taken at operation, and were changed to organism-specific therapy when culture results were available. Parenteral antibiotics were continued for a mean of five weeks (range, two to eight weeks) and seven of 13 patients received oral antibiotics for an additional two to six weeks after parenteral therapy. Bone grafting or muscle flaps or both were used in those patients with compromised structural integrity, or to fill created dead space and allow wound closure. In postoperative follow-up evaluation, none of the patients have had evidence for recurrent osteomyelitis (mean duration, 58 months; range, 27-89 months). This technique of serial operations with proper antimicrobial therapy, followed by bone grafting and local muscle flaps when needed, has led to excellent end results in the treatment of chronic osteomyelitis.

Adult↗
PubMed1993

Phototrapping of doubly reduced monomeric bacteriochlorophyll in the photoreaction center of Ectothiorhodospira sp.

The photoreaction center from the purple sulfur bacterium Ectothiorhodospira sp. was illuminated in the presence of reduced cytochrome c or dithionite under anaerobic conditions. This treatment first caused the monoelectronic reduction of both molecules of bacteriopheophytin (Bph), phi A and phi B, as witnessed by the appearance of EPR and optical signals typical of singly-reduced bacteriochlorins. Continued illumination under the same reducing conditions caused both of these signals to disappear. Such disappearance was accompanied by a complete bleaching of the Qx and Qy absorption bands of Bph but not of the corresponding transitions of bacteriochlorophyll (Bchl). These phenomena are interpreted by a double reduction of phi A and phi B. As long as the medium remained reducing and anaerobic, these changes were stable. Prolonged illumination under the same reducing conditions finally led to the bleaching of the Qx (600 nm) and Qy (800 nm) bands of Bchl but not of the 880-nm band. This generated no EPR or 645-nm absorption signals due to singly-reduced Bchl. The bleaching kinetics of the 800-nm band was biphasic and paralleled a shift of the peak wavelength. This is interpreted by a double reduction of both molecules of monomeric Bchl BA and BB in an undetermined order. After bleaching of the 800-nm band has reached saturation, the absorbance ratio of the 800/880-nm absorption bands remains constant, as would be expected if the ultimate spectrum was that of the primary electron donor. These experiments demonstrate the photoreduction of Bchl and allow the absorption spectrum of the primary donor to be measured for the first time.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaerobiosis↗
PubMed1993

Physical injury risk versus risk from hazardous waste remediation: a case history.

This study was conducted to estimate the transportation risks associated with the removal of contaminated soils near the ASARCO copper smelter in Ruston, Washington. Three remediation options involving removal of differing amounts of soil were considered. The risks of death, disabling, and nondisabling injury were estimated. Under the scenario requiring the greatest soil removal, 3.62 disabling injuries, 14.46 possibly disabling injuries, and 0.67 deaths are expected to result from transporting the contaminated soil to an approved hazardous waste disposal facility. If the contaminated soil is not removed, the U.S. Environmental Protection Agency estimates that 2 arsenic-related skin cancers per 1000 lifetimes for exposed persons will occur.

Accidents, Traffic↗
PubMed1985

Use of computerized pattern recognition in the study of the cuticular hydrocarbons of imported fire ants. I. Introduction and characterization of the cuticular hydrocarbon patterns of Solenopsis invicta and S. richteri.

A method is described in which gas chromatographic (GC) data obtained from cuticular hydrocarbons are treated by methods of pattern recognition. Based on a recently described sample preparation procedure, GC data are normalized to eliminate slight variations in chromatographic conditions and converted into the proper format for discriminant analysis by computer. The results of several methods of data treatment and display are discussed, based upon the chemometric system package, ARTHUR. The approach has the advantage of largely removing operator bias.

Animals↗
PubMed1985

Use of computerized pattern recognition in the study of the cuticular hydrocarbons of imported fire ants. II. Comparison of the cuticular hydrocarbon patterns between different colonies of Solenopsis richteri.

Gas chromatography (GC) data obtained from the cuticular hydrocarbons of the black imported fire ants are treated by methods of pattern recognition. Based on a recently described sample preparation procedure, GC data are normalized to eliminate slight variations in chromatographic conditions, and converted to the proper format for discriminant analysis by computer. The results of several methods of data treatment and display are discussed, based on the chemometrics system package, ARTHUR.

Animals↗
PubMed1981

Measurement of mitochondrial volume independent of refractive index by light scattering.

Using latex spheres of accurately determined dimensions, it was found that, although the scattered light intensity at an angle within the forward scattering lobe varies with the refractive index of the medium, the ratio of the scattered light intensity at a pair of angles is independent of the refractive index. This finding is consistent with calculations from the Mie theory by Hodkinson that the shape of the forward scattering lobe depends only on the size of the sphere and is independent of the refractive index of the sphere or of the suspending medium. This method was applied to the measurement of volume changes in mitochondria induced either by suspending the mitochondria in solutions of different osmolality or by addition of ionophores to stimulate ion uptake. The volume changes measured were independent of the refractive index of the suspending medial. It is shown that measuring the ratio of the scattered light intensity at selected pair of angles within the forward scattering lobe is a good method to measure the average size of the mitochondria.

Animals↗
PubMed1977

Evidence for monomeric bacteriochlorophyll in P800 of the photoreaction center from Rhodospirillum rubrum.

To find out whether weak or strong coupling exists between the bacteriochlorophyll molecules of the photoreaction center, the relative efficiency of energy transfer to P870 was measured at 795 nm and at 808 nm, at room temperature and at 77 degrees K. At room temperature, both relative efficiencies are close to 100%. However, at 77 degrees K, 795 nm light has a quantum efficiency of 76% and 808 nm light has an efficiency of 87%. These results confirm the fact that P800 is formed of at least one short wavelength component and one long wavelength component. Moreover, the short wavelength component is weakly coupled to both P870 and to the long wavelength component of P800. The conclusion is that the short wavelength component is due to monomeric bacteriochlorophyll. By comparison with other data, all four bacteriochlorophyll molecules of the photoreaction center are inferred to be monomeric.

Bacteriochlorophylls↗
PubMed1976

Photodichroic studies of the photoreaction center from Rhodospirillum rubrum. I. Attribution of P870 to two non parallel dipoles.

A randomly oriented sample of photoreaction center prepared from Rhodospirillum rubrum was excited at 77 degrees K by an actinic linearly polarized light of 870 nm. Under such conditions, only those chromophores with components of their absorption dipoles oriented parallel to the polarization of the actinic light are bleached. The change in absorbance at 900 nm of this photoselected sample was observed while varying the angle of polarization of a weak measuring light. The polarization of the absorbance change was thus evaluated as 0.25. This value is interpreted to mean that P870 is attributable to two absorption dipoles forming an angle included between 35.75 degrees and 90 degrees. Comparison with the p value of 0.5 obtained on a similar preparation by polarization of fluorescence (Ebrey, T. G. and Clayton, R.K. (1969) Photochem. Photobiol. 10, 109-117) leads to the conclusion that either these two dipoles emit fluorescence without being coupled by singlet-singlet energy transfer or that only one of them is a fluorescence emitter in the absence of reversible singlet-singlet energy transfer.

Cytochromes↗
PubMed1975

Induction kinetics of delayed light emission in spinach chloroplasts.

Induction curves of the delayed light emission in spinach chloroplasts were studied by measuring the decay kinetics after each flash of light. This study differs from previous measurements of the induction curves where only the intensities at one set time after each flash of light were recorded. From the decay kinetics after each flash of light, the induction curves of the delayed light emission measured 2 ms after a flash of light were separated into two components: one component due to the last flash only and one component due to all previous flashes before the last one. On comparing the delayed light induction curves of the two components with the fluorescence induction curves in chloroplasts treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea and in chloroplasts treated with hydroxylamine and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, the component due to the last flash only is found to be dependent on the concentration of open reaction centers and the component due to all previous flashes except the last is dependent on the concentration of closed reaction centers. This implies that the yield of the fast decaying component of the delayed light emission is dependent on the concentration of open reaction centers and the yield of the slow decaying component is dependent on the concentration of closed reaction centers.

Chloroplasts↗
PubMed1972

Lifetime of the excited state in vivo. I. Chlorophyll a in algae, at room and at liquid nitrogen temperatures; rate constants of radiationless deactivation and trapping.

Using a mode-locked laser (lambda, 632.8 nm), fluorescence decay of chlorophyll (Chl) a in the green alga Chlorella pyrenoidosa, the red alga Porphyridium cruentum, and the blue-green alga Anacystis nidulans was measured by the phase-shift method under conditions when photosynthesis was not operative (3-(3,4-dichlorophenyl)-1,1-dimethylurea [DCMU] poisoning, or cooling to 77 degrees K). In the presence of 10(-5) M DCMU, the lifetime of Chl a fluorescence (tau) at room temperature is about 1.7 nsec in Chlorella, 1.0 nsec in Porphyridium, and 0.7 nsec in Anacystis. At 77 degrees K, tau is 1.4 nsec (for fluorescence at about 685 nm, F-685) and 2.3 nsec (for F-730) in Chlorella, 0.9 nsec (F-685) and 1.2 nsec (F-730) in Porphyridium, and 0.8 nsec (F-685 and F-730) in Anacystis. From the above measurement, and the assumption that tau(0) (the intrinsic fluorescence lifetime) for Chl a in all three algae is 15.2 nsec, we have calculated the rate constants of radiationless transition (that includes energy transfer to weakly fluorescent system I) processes competing with fluorescence at room temperature to be about 5 x 10(8) sec(-1) in Chlorella, 9 x 10(8) sec(-1) in Porphyridium, and 13 x 10(8) sec(-1) in Anacystis. At 77 degrees K, this rate constant for Chl a that fluoresces at 685 nm remains, in the first approximation, the same as at room temperature. From the tau data, the rate constant for the trapping of excitation energy is calculated to be about 1.2 x 10(9) sec(-1) for Chlorella, 2 x 10(9) sec(-1) for Porphyridium, and 2 x 10(9) sec(-1) for Anacystis. The efficiency of trapping is calculated to be about 66% (Chlorella), 68% (Porphyridium), and 60% (Anacystis). (It is recognized that variations in the above values are to be expected if algae grown under different conditions are used for experimentation.) The maximum quantum yield of Chl a fluorescence for system II (lambda, 632.8 nm), calculated from tau measurements, is about 10% in Chlorella, 6-7% in Porhyridium, and 5% in Anacystis under conditions when photosynthesis is not operative; the values at 77 degrees K appear to be very close to those with DCMU added at room temperature. ø for F-730 at 77 degrees K, however, is somewhat higher than for F-685. The predicted quantum yields of fluorescence for Chl a in intact cells (both systems I and II) at low intensities of 632.8 nm light are about 2-3, 1-2, and 1% for Chlorella, Porphyridium, and Anacystis, respectively.

Chlorella↗
PubMed1969

Mode-locked lasers: measurements of very fast radiative decay in fluorescent systems.

A mnode-locked laser was used to measure fluorescence decay down to 80 picoseconds. Measurements on the fluorescence of methylene blue quenchled with potassium iodide demonstrate the effectiveness of the method. Fluorescence decay times of chlorophyll b (3.87 +/- 0.05 nianoseconds) and c-phycocyanin (1.14 +/- 0.01 nanoseconds) in vitro and chlorophyll a in the green alga Chlorella pyrenoidosa (1.14 to 1.6 nanoseconds) compare well with some of the existing data.

Antimetabolites↗