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Biomedical subjects

R Rieder

Publications and source records attributed to R Rieder.

At least 19 recordsLinked to original sources
PubMed2000

Curium-244 alpha-sources for space research

Special alpha-proton-X-ray spectrometric complexes (APXS) have been developed in order to perform chemical analyses of the Mars atmosphere and rock surface compounds by alpha back-scattering, alpha-proton measurements, and X-ray fluorescence. The sources were prepared by high temperature condensation of metal curium vapour onto silicon substrates. They are silicon disks with curium-244 fixed on their surfaces as a silicide. The sources have overall dimensions as follows: disk diameter 8 mm; thickness 0.3 mm; and 6 mm diameter active spot. The source activities are 5 +/- 1 mCi and the alpha-line half-widths are equal to (1.7-2.5) and (2.9-4.5)% of full width at 10% of Maximum (Maximum is equal to 5.8 MeV). Thermovacuum (from 196 to 1000 degrees C), mechanical, and resource tests were performed and demonstrated that the sources maintained their characteristics. The applicability of the sources for the above-mentioned analytical purposes was confirmed during NASA Mars Pathfinder mission.

Journal Article↗
PubMed1997

Overview of the Mars Pathfinder mission and assessment of landing site predictions.

Chemical analyses returned by Mars Pathfinder indicate that some rocks may be high in silica, implying differentiated parent materials. Rounded pebbles and cobbles and a possible conglomerate suggest fluvial processes that imply liquid water in equilibrium with the atmosphere and thus a warmer and wetter past. The moment of inertia indicates a central metallic core of 1300 to 2000 kilometers in radius. Composite airborne dust particles appear magnetized by freeze-dried maghemite stain or cement that may have been leached from crustal materials by an active hydrologic cycle. Remote-sensing data at a scale of generally greater than approximately 1 kilometer and an Earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic floods that are relatively dust-free.

Atmosphere↗
PubMed1997

The chemical composition of Martian soil and rocks returned by the mobile alpha proton X-ray spectrometer: preliminary results from the X-ray mode.

The alpha proton x-ray spectrometer (APXS) on board the rover of the Mars Pathfinder mission measured the chemical composition of six soils and five rocks at the Ares Vallis landing site. The soil analyses show similarity to those determined by the Viking missions. The analyzed rocks were partially covered by dust but otherwise compositionally similar to each other. They are unexpectedly high in silica and potassium, but low in magnesium compared to martian soils and martian meteorites. The analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of Earth's crust. Addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition.

Aluminum↗
PubMed1995

1995 Volvo Award in clinical sciences. The diagnostic accuracy of magnetic resonance imaging, work perception, and psychosocial factors in identifying symptomatic disc herniations.

STUDY DESIGN: This was a prospective study of patients (study group) with symptomatic disc herniations and asymptomatic volunteers (control group) matched for age, sex, and work-related risk factors. OBJECTIVE: To determine the prevalence of disc herniation in a matched group of asymptomatic volunteers and to access the diagnostic accuracy of magnetic resonance imaging, work perception, and psychosocial factors in identifying symptomatic disc herniations. SUMMARY OF BACKGROUND DATA: Disc herniations have been reported to occur in 20-36% of asymptomatic volunteers. A valid comparison of asymptomatic individuals and patients with disc herniations has not been performed. METHODS: Forty-six patients with low back pain and sciatica severe enough to require a discectomy were compared with 46 age-, sex-, and risk factor-matched (heavy lifting, twisting and bending, vibration, and sedentary activity) asymptomatic volunteers. Both groups had a complete clinical and magnetic resonance imaging examination and completed a questionnaire to assess differences in the psychosocial and work perception profiles. The prevalence and the severity of morphologic alterations (disc herniation, disc degeneration, and neural compromise) was analyzed by tow independent radiologists in a blinded fashion. Differences between both groups regarding MRI findings, work perception (occupational mental stress, intensity of concentration, job satisfaction, and job-related resignation) and psychosocial factors (anxiety, depression, self-control, social support, and marital status) were compared using multivariate techniques. Stepwise discriminating analysis was used to identify the best discriminating variables within the magnetic resonance image, work perception, and psychosocial categories in terms of the diagnostic accuracy to predict group membership (study [pain] or control [no pain] group). RESULTS: Matched controls had significantly more risk factors than a group of normal individuals. The present study has presented evidence that an age-, gender-, and occupational risk factors-matched group of asymptomatic patients shows a high incidence rate of disc herniations (76%). Although significantly less than the symptomatic group incidence of 96%, this represents a much higher prevalence rate than generally expected and reported in other studies of unmatched asymptomatic volunteers. Patients had more severe disc herniations (disc extrusions) than asymptomatic volunteers (35% vs. 13%). There was no significant differences regarding disc degeneration between both groups (96% vs. 85%). The only substantial morphologic difference between both groups was the presence of a neural compromise (83% vs. 22%), which was highly significant (P < 0.0001). There were significant differences between both groups regarding work perception (occupational mental stress, intensity of concentration, job satisfaction, and resignation; P < 0.027) and psychosocial factors (anxiety, depression, self-control, marital status; P < 0.0001). The best single predictor of a group membership was the extent of neural compromise. A combination of this factor with occupational mental stress, depression, and marital status was the best predictive model. With this model, the false-negative rate (potential overtreatment of disc morphology) was reduced by more than half compared with morphologic factors (nerve root compression) alone (22% vs. 11%). CONCLUSIONS: In an age-, sex-, and risk factor-matched group of asymptomatic individuals, disc herniation had a substantially higher prevalence (76%) than previously reported in an unmatched group. Individuals with minor disc herniations (i.e., protrusion, contained discs) are at a very high risk that their magnetic resonance images are not a causal explanation of pain because a high rate of asymptomatic subjects (63%) had comparable morphologic findings. The only highly significant difference between the study group and control group regarding morphologic fi

Adult↗
PubMed1985

Binding of cytochrome c2 to the isolated reaction center of Rhodospirillum rubrum involves the "backside" of cytochrome c2.

Lys 109, Lys 112 and Glu 1 of cytochrome c2 from Rhodospirillum rubrum G-9 are about 4-fold less reactive towards acetic anhydride when cytochrome c2 is bound to the isolated photosynthetic reaction center from the same organism. The three shielded residues are clustered together on the "backside" of cytochrome c2. This contrasts with mitochondrial cytochrome c where "frontside" lysines are protected by different physiological electron transfer partners.

Acetylation↗
PubMed1984

Purification and properties of the soluble hydrogenase from Desulfovibrio desulfuricans (strain Norway 4).

A soluble hydrogenase has been isolated from Desulfovibrio desulfuricans (strain Norway 4) grown on Postgate's medium. The enzyme differs significantly from a membrane-bound hydrogenase previously purified from the same organism grown on Starkey's medium. The enzyme consisted of two subunits of 56 kDa and 29 kDa compared with masses of 60 kDa and 27 kDa for the membrane-bound enzyme. Analysis of preparations of the soluble enzyme by various methods gave values of 5-10 iron atoms, 6 labile sulphur atoms and 0.45-0.8 nickel atom per molecule. The enzyme was unusual in that it contained selenium, in quantities equivalent to nickel. The highly purified active enzyme produced no electron-spin-resonance (ESR) signals in the oxidized state. ESR signals due to a [3Fe-xS] cluster and nickel were observed only in some of the less active fractions of the enzyme, demonstrating that neither of these ESR-detectable components is a prerequisite for hydrogenase activity. Treatment of D. desulfuricans (Norway) cells with EDTA released a minor fraction with hydrogenase activity, which might indicate the presence of a periplasmic enzyme.

Amino Acids↗
PubMed1984

Spectroscopic studies of the nature of the iron clusters in the soluble hydrogenase from Desulfovibrio desulfuricans (strain Norway 4).

57Fe-enriched samples of the soluble hydrogenase from Desulfovibrio desulfuricans (Norway) have been investigated in both the native (oxidized) and the dithionite-reduced states using Mössbauer spectroscopy. The data clearly show that the iron in this enzyme is predominantly in the form of iron-sulphur clusters which are closely similar to the [4Fe-4S] clusters found in a large number of ferredoxins, such as that from Bacillus stearothermophilus. There appear to be two [4Fe-4S] clusters. The iron-sulphur clusters in the oxidized protein are virtually diamagnetic, as indicated by Mössbauer, electron spin resonance and magnetic circular dichroic spectroscopy. On reduction by dithionite + methyl viologen, Mössbauer spectroscopy showed that only 50% of the [4Fe-4S] clusters were reduced. Even reduction with hydrogen up to a pressure of 23 GPa did not reduce the iron-sulphur clusters completely. An ESR signal due to a rapidly relaxing species with g = 2.03, 1.89 was observed in the reduced protein, together with a weaker spectrum from a slower-relaxing species at g = 2.34, 2.12.

Chemical Phenomena↗
PubMed1981

Some aspects of the pathophysiology of homozygous Hb CC erythrocytes.

We have studied erythrocytes from homozygous CC patients in vitro and in perfused rat mesoappendix vasculature to answer some long-standing questions. By examination of wet whole blood preparations, and by comparing the cell distribution on isopycnic continuous density gradients of whole blood samples from a splenectomized CC patient with those from three intact CC patients, we have demonstrated the presence of a distinct crystal-containing band of cells that is present in the former, but totally absent from the latter. We conclude that Hb CC cells containing crystals circulate in Hb CC individuals, but in intact patients they are effectively removed by the spleen. By use of 31P nuclear magnetic resonance and viscosity measurements on cells, we have demonstrated that intracellular aggregation of hemoglobin C occurs on deoxygenation even when no crystal formation is detectable by morphological methods. These two observations are in apparent contradiction with the absence of clinical microcirculatory impairment found in both intact and splenectomized CC patients. The contradiction was resolved by rheological studies on isolated rat mesoappendix preparations and erythrocyte diameter measurements that lead to the conclusion that the hemorheological properties of CC cells in the microcirculation are nearly normal because their increased viscosity is offset by their smaller diameter and size.

Blood Viscosity↗
PubMed1980

Comparison of the binding sites on cytochrome c for cytochrome c oxidase, cytochrome bc1, and cytochrome c1. Differential acetylation of lysyl residues in free and complexed cytochrome c.

The isolated complexes of ferricytochrome c with cytochrome c oxidase, cytochrome c reductase (cytochrome bc1 or complex III), and cytochrome c1 (a subunit of cytochrome c reductase) were investigated by the method of differential chemical modification (Bosshard, H.R. (1979) Methods Biochem. Anal. 25, 273-301). By this method the chemical reactivity of each of the 19 lysyl side chains of horse cytochrome c was compared in free and in complexed cytochrome c and binding sites were deduced from altered chemical reactivities of particular lysyl side chains in complexed cytochrome c. The most important findings follow. 1. The binding sites on cytochrome c for cytochrome c oxidase and cytochrome c reductase, defined in terms of the involvement of particular lysyl residues, are indistinguishable. The two oxidation-reduction partners of cytochrome c interact at the front (exposed heme edge) and top left part of the molecule, shielding mainly lysyl residues 8, 13, 72 + 73, 86, and 87. The chemical reactivity of lysyl residues 22, 39, 53, 55, 60, 99, and 100 is unaffected by complex formation while the remaining lysyl residues in positions 5, 7, 25, 27, 79, and 88 are somewhat less reactive in the complexed molecule. 2. When bound to cytochrome c reductase or to the isolated cytochrome c1 subunit of the reductase the same lysyl side chains of cytochrome c are shielded. This indicates that cytochrome c binds to the c1 subunit of the reductase during the electron transfer process.

Animals↗