Tunneling in Chromatium chromatophores: Detection of a Hopfield charge-transfer band

We have observed a weak charge-transfer band in the cytochrome c-P(870) electron-transfer reaction in Chromatium vinosum chromatophores at 10 K and at 85 K. First, the intermediate acceptor, I, was trapped in the reduced state by lowering the redox potential at room temperature, then illuminating with white light at low temperature for 20 min. Next, illumination by broadband infrared (1-3 mum, 6.5 kW/m(2)) for 4 hr at 10 K decreased the I(-) electron spin resonance signal by 30%. One-hour infrared illumination at 85 K decreased the cytochrome c Soret band shift by 10%. The effect of infrared was to promote the system from the ground vibrational state with the electron on P(870) to an excited vibrational state with the electron on cytochrome c. The absorption band peak is near 2 mum, and the integrated cross section is approximately 6 x 10(-3) eV.M(-1).cm(-1). These values are consistent with small (0.02 nm) nuclear motion and with electron-transfer rates measured in the dark.

cDNA cloning, in vitro expression, and biochemical characterization of cholinesterase 1 and cholinesterase 2 from amphioxus--comparison with cholinesterase 1 and cholinesterase 2 produced in vivo

We have isolated cDNAs coding for the complete amino acid sequences of cholinesterase 1 (ChE1) and cholinesterase 2 (ChE2) from amphioxus. Both ChE transcripts have the characteristics of H-type catalytic subunits, which are inserted in the membrane via an ethanolamine-glycan-phosphatidylinositol anchor. The members of the catalytic triad of ChEs, the three pairs of cysteine residues involved in intrachain disulfide bonding, a cysteine near the carboxy terminal of both sequences, which could mediate interchain disulfide bonding, and 11 of the 14 aromatic amino acids that line the catalytic gorge of AChE are conserved. A remarkable difference between the two enzymes is in the region of the acyl-binding pocket, which plays an important role in determining substrate specificity in cholinesterases. ChE2 contains a sequence that resembles the acyl pocket of invertebrate ChE, while the acyl-binding site of ChE1 is novel. There are also differences between the two enzymes in the peripheral anionic site, which mediates inhibition by certain ligands. In vitro expression in COS-7 cells demonstrates that ChE2 hydrolyzes acetylthiocholine almost exclusively, while ChE1 hydrolyzes both acetylthiocholine and butyrylthiocholine. Both enzymes are inhibited comparably by BW284c51, but ChE1 is considerably more resistant to inhibition by propidium, ethopropazine, and eserine than is ChE2. Velocity sedimentation indicates that ChE1 and ChE2 are present as amphiphilic and nonamphiphilic G2 forms in vivo and in vitro. Another molecular form, which sediments at 17 S, is also present in vivo. Nondenaturing gel electrophoresis in conjunction with digestion by phosphatidylinositol-specific phospholipase C demonstrates that the vast majority of ChE1 and ChE2 is present as ethanolamine-glycan-phosphatidylinositol-anchored G2 forms in vivo. ChE1 also possesses an ethanolamine-glycan-phosphatidylinositol-anchor in vitro; however, ChE2 produced in vitro could not be detected on nondenaturing gels.

Occupationally related cancer risk among coke oven workers: 30 years of follow-up

This study concerns the update of cause-specific mortality among coke oven workers. Updated information provides 3 decades of work history and vital status follow-up on 15,818 workers. Mortality patterns are summarized by race, cumulative exposure, and period of follow-up. The findings are consistent with those from earlier assessments, indicating that occupational exposure to coke oven emissions is associated with significant excess mortality from cancer of the respiratory system and of the prostate. Depending on the segment of the population considered, the respiratory cancer risk for coke oven workers ranged as high as 4.45 times that for non-oven workers. Relative risk values for cancer of the prostate ranged as high as 1.93. Rates of respiratory cancer across period of follow-up are declining, suggesting that the implementation of emissions control and occupational exposure limits has been beneficial.

Laser-feedback measurements of turtle basilar membrane motion using direct reflection

In mammalian hearing, the frequency-dependent spatial pattern of movement in the basilar membrane/organ of Corti complex forms the basis of frequency discrimination. This is not necessarily the case in lower vertebrates; the turtle, for example, has an electrical resonance mechanism in its auditory receptor cells that varies in best frequency from cell to cell. But how much, if any, of the frequency separation by the turtle is done mechanically by the basilar membrane complex? Attempts to find an investigative approach that avoided placing objects on the basilar membrane led to the rediscovery of laser-feedback interferometry. Laser-feedback interferometric investigations of the vibrational amplitude and phase of the turtle basilar membrane in response to imposed nanometer displacements of the eardrum reveal that the membrane reflects the broadly-tuned middle-ear filter characteristics. Phase-angle measurements of the basilar membrane as a function of frequency, and the best frequency of the obtained amplitude tuning curves, did not vary as a function of position within each specimen. Input-output functions of the basilar membrane were generally linear. The middle ear demonstrates a negative gain of 2-6 while the central region of the basilar membrane has a positive gain of 4-18 dependent on location and biological variability.

PHOEBE, a prototype scanning laser-feedback microscope for imaging biological cells in aqueous media

Based on the principle of laser-feedback interferometry (LFI), a laser-feedback microscope (LFM) has been constructed capable of providing an axial (z) resolution of a target surface topography of approximately 1 nm and a lateral (x,y) resolution of approximately 200 nm when used with a high-numerical-aperture oil-immersion microscope objective. LFI is a form of interferometry in which a laser's intensity is modulated by light re-entering the illuminating laser. Interfering with the light circulating in the laser resonant cavity, this back-reflected light gives information about an object's position and reflectivity. Using a 1-mW He-Ne (lambda = 632.8 nm) laser, this microscope (PHOEBE) is capable of obtaining 256 x 256-pixel images over fields from (10 microns x 10 microns) to (120 microns x 120 microns) in approximately 30 s. An electromechanical feedback circuit holds the optical pathlength between the laser output mirror and a point on the scanned object constant; this allows two types of images (surface topography and surface reflectivity) to be obtained simultaneously. For biological cells, imaging can be accomplished using back-reflected light originating from small refractive-index changes (> 0.02) at cell membrane/water interfaces; alternatively, the optical pathlength through the cell interior can be measured point-by-point by growing or placing a cell suspension on a higher-reflecting substrate (glass or a silicon wafer).(ABSTRACT TRUNCATED AT 250 WORDS)

Patient perspectives on computer-based medical records

BACKGROUND

Despite emerging interest in computer-based patient records (CPRs), less than 1% of medical records in the United States are stored electronically. Some physicians may be reluctant to implement CPR systems because of fear that the physician-patient relationship would be adversely affected. This study ascertained the attitudes of patients regarding the use of CPR systems.

METHODS

This study was an in-depth interview survey of 16 patients concerning the CPR system used at the family medicine department at the Medical University of South Carolina. Interview topics included patient knowledge, perceived advantages and disadvantages, and the impact of the CPR system on their relationship with their physician.

RESULTS

Most patients were informed about the nature of the CPR system and had positive attitudes toward it. Common perceptions were that CPR provides physicians with easy access to information, facilitates clinical encounters, and improves physician-patient relationship and the quality of care delivered. Although confidentiality was the major concern expressed about the CPR system, only one respondent indicated that this factor limited his interaction with his physician.

CONCLUSIONS

This study demonstrated patient acceptance and support for the CPR system in use at the study site. These findings should encourage physicians to use CPRs.

Electron paramagnetic resonance saturation studies of P-700+ reaction center chlorophyll in plant photosynthesis

Electron paramagnetic resonance (EPR) power saturation and saturation recovery methods have been used to determine the spin lattice, T1, and spin-spin, T2, relaxation times of P-700+ reaction-center chlorophyll in Photosystem I of plant chloroplasts for 10 K less than or equal to T less than or equal to 100 K. T1 was 200 mus at 100 K and increased to 900 mus at 10 K. T2 was 40 ns at 40 K and increased to 100 ns at 10 K. T1 for 40 K less than or equal to T less than or equal to 100 K is inversely proportional to temperature, which is evidence of a direct-lattice relaxation process. At T = 20 K, T1 deviates from the 1/T dependence, indicating a cross relaxation process with an unidentified paramagnetic species. The individual effects of ascorbate and ferricyanide on T1 of P-700+ were examined: T1 of P-700+ was not affected by adding 10 mM ascorbate to digitonin-treated chloroplast fragments (D144 fragments). The P-700+ relaxation time in broken chloroplasts treated with 10 mM ferricyanide was 4-times shorter than in the untreated control at 40 K. Ferricyanide appears to be relaxing the P-700+ indirectly to the lattice by a cross-relaxation process. The possibility of dipolar-spin broadening of P-700+ due to either the iron sulfur center A or plastocyanin was examined by determining the spin-packet linewidth for P-700+ when center A and plastocyanin were in either the reduced or oxidized states. Neither reduced center A nor oxidized plastocyanin was capable of broadening the spin-packet linewidth of P-700+ signal. The absence of dipolar broadening indicates that both center A and plastocyanin are located at a distance at least 3.0 nm from the P-700+ reaction center chlorophyll. This evidence supports previous hypotheses that the electron donor and acceptor to P-700 are situated on opposite sides of the chloroplast membrane. It is also shown that the ratio of photo-oxidized P-700 to photoreduced centers A and B at low temperature is 2 : 1 if P-700 is monitored at a nonsaturating microwave power.