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R Conrad

Publications and source records attributed to R Conrad.

At least 91 records · Page 5Linked to original sources
PubMed1988

Influence of pH on microbial hydrogen metabolism in diverse sedimentary ecosystems.

Hydrogen transformation kinetic parameters were measured in sediments from anaerobic systems covering a wide range of environmental pH values to assess the influence of pH on hydrogen metabolism. The concentrations of dissolved hydrogen were measured and hydrogen transformation kinetics of the sediments were monitored in the laboratory by monitoring hydrogen consumption progress curves. The hydrogen turnover rate constants (kt) decreased directly as a function of decreasing sediment pH, and the maximum hydrogen uptake velocities (Vmax) varied as a function of pH within each of the trophic states. Conversely, the half-saturation concentrations (Km) were independent of pH. The steady-state hydrogen concentrations were at least 2 orders of magnitude lower than the half-saturation constants for hydrogen uptake. Dissolved hydrogen concentrations were at least fivefold higher in sediments from eutrophic systems than from oligotrophic and dystrophic systems. The rates of hydrogen production determined from the assumption of steady state decreased with sediment pH. These data indicate that progressively lower pH values inhibit microbial hydrogen-producing and -consuming processes within sedimentary ecosystems.

Bacteria, Anaerobic↗
PubMed1988

Prevalence of hepatitis B markers among pregnant Hispanic women in migrant/seasonal work in Oregon.

We screened 303 Hispanic pregnant women who were migrant or seasonal agricultural workers in Oregon for the presence of Hepatitis B serological markers. One carrier was identified (0.3 per cent, 95% confidence interval [CI] .02%, 2.1%). Evidence of previous HB infection was present in 5.3 per cent (16/303) of the women (95% CI 3.2%, 8.6%), rates similar to those for the general US population.

Adolescent↗
PubMed1984

Physiological function of hydrogen metabolism during growth of sulfidogenic bacteria on organic substrates.

Desulfovibrio vulgaris Madison and Thermodesulfobacterium commune contained functionally distinct hydrogenase activities, one which exchanged 3H2 into 3H2O and was inhibited by carbon monoxide and a second activity which produced H2 in the presence of CO. Cell suspensions of D. vulgaris used either lactate, pyruvate, or CO as the electron donor for H2 production in the absence of sulfate. Both sulfidogenic species produced and consumed hydrogen as a trace gas during growth on lactate or pyruvate as electron donors and on thiosulfate or sulfate as electron acceptors. Higher initial levels of hydrogen were detected during growth on lactate-sulfate than on pyruvate-sulfate. D. vulgaris but not T. commune also produced and then consumed CO during growth on organic electron donors and sulfate or thiosulfate. High partial pressures of exogenous H2 inhibited growth and substrate consumption when D. vulgaris was cultured on pyruvate alone but not when it was metabolizing pyruvate plus sulfate or lactate plus sulfate. The data are discussed in relation to supporting two different models for the physiological function of H2 metabolism during growth of sulfidogenic bacteria on organic electron donors plus sulfate. A trace H2 transformation model is proposed for control of redox processes during growth on either pyruvate or lactate plus sulfate, and an obligate H2 cycling model is proposed for chemiosmotic energy coupling during growth on CO plus sulfate.

Bacteria↗
PubMed1979

Evaluation of the efficiency of extraction for the quantitative estimation of hydrogen bacteria in soil.

The efficiency of extraction of hydrogen bacteria from soil for plate counting was evaluated by using pure cultures adsorbed to sterilized soil. The utilization of model materials which interact with bacteria by adhesive, capillary or electrostatic forces and the use of extraction fluids with buffering, detergent or chelating activity demonstrated the major importance of capillary forces for the retention of hydrogen bacteria. Utilization of Tris buffer (pH 7.5) as extraction fluid and separation of extracted bacteria from soil particles by sedimentation for 15 min resulted in the highest recovery. A second extraction step including sonication did not increase the efficiency. The extraction efficiency of 8 different strains of hydrogen bacteria adsorbed to 3 different soils demonstrated a high degree of variation wih respect to bacterial strains, but not to soil types. The recovery was inversely related to cell parameters such as size, motility and slime formation.

Adsorption↗
PubMed1978

Metabolism of fructose in Thiocapsa roseopersicina.

Thiocapsa roseopersicina strain 6311 grew phototrophically in a mineral medium containing fructose as sole electron donor and carbon source with a doubling time of 11--13 h, provided the mineral medium contained vitamine B12 (50 ng/ml), not more than 20 mM phosphate, and the culture was preincubated in the dark for 24 h. In fructose-grown cells but not in autotrophically grown cells, the cell-protein content was strongly reduced when vitamine B12 was growth limiting, while the carbohydrate content was increased. Growth on fructose as sole carbon source was inhibited by the addition of sulfide or thiosulfate; growth inhibition was relieved in the presence of bicarbonate. No growth on fructose was observed anaerobically in the dark; aerobic growth in the dark was poor. Analysis of enzyme activities in fructose- and acetate-grown cells indicated that fructose was catabolized via fructose-1-phosphate and the EMBDEN-MEYERHOF pathway. The operation of the EMBDEN-MEYERHOF pathway was confirmed by incorporation of 1-14C-, 3-14C-, and 6-14C-fructose into the spirilloxanthin fraction and analysis of its specific radioactivity.

Aerobiosis↗
PubMed1978

An alternative pathway for the degradation of endogenous fructose during the catabolism of sucrose in Rhodopseudomonas capsulata.

Sucrose catabolism was studied in Rhodopseudomonas capsulata. Sucrose was hydrolysed by the action of a constitutive cytoplasmic sucrase. The use of a glucose-6-phosphate dehydrogenase-deficient mutant and radiorespirometric experiments demonstrated that both the glucose and fructose moieties of sucrose were catabolized via the Entner-Doudoroff pathway. This result was confirmed by enzyme analysis and studies on sugar assimilation. All the enzymes of the Entner-Doudoroff pathway were present in bacteria grown on secrose but fructokinase (EC 1.7.1.4) activity was relatively low. In contrast, phosphoenolpyruvate:fructose phosphotransferase and 1-phosphofructokinase, the key enzymes for the catabolism of exogenous fructose, were only partially induced. Bacteria grown on sucrose and treated with chloramphenicol were, therefore, not able to assimilate exogenous fructose. We conclude that under these conditions endogenous fructose is catabolized via the Entner-Douboroff pathway, while exogenous fructose is degraded via fructose 1-phosphate and the Embden-Meyerhof pathway.

Fructose↗
PubMed1978

Regulation of glucose, fructose and sucrose catabolism in Rhodopseudomonas capsulata.

Regulation of glucose, fructose and sucrose catabolism was studied in Rhodopseudomonas capsulata grown under phototrophic conditions. The sequence of preference for the utilization of the sugar substrates was fructose, glucose, sucrose. The presence of a preferred substrate did not completely suppress the utilization of the less preferred. Glucose-6-phosphate dehydrogenase, the key enzyme of glucose and sucrose catabolism, exhibited sigmoidal substrate saturation curves and was inhibited by phosphoenolpyruvate, whereas 1-phosphofructokinase, the key enzyme of fructose catabolism, exhibited hyperbolic substrate saturation curves and was not inhibited by phosphoenolpyruvate. Since phosphoenolpyruvate is a common intermediate of glucose, fructose and sucrose catabolism, the control of glucose-6-phosphate dehydrogenase may be responsible for the preferential utilization of fructose.

Fructose↗
PubMed1977

Conversion of oxy- into methemerythrin in the presence of anions.

The interaction of oxyhemerythrin (HrO2) with cyanate and azide ions (X-) is biphasic. The rapid loss of HrO2 is monitored at 500 nm using stopped flow. The dependence of the pseudo-first order rate constant on [HrO2], [X-], and [O2] can be interpreted by the scheme HrO2 in equilibrium Hr + O2 K1 Hr + X-in equilibrium HrX- k2, k-2, k2 At 25 degrees, pH = 6.3 and I = 0.15 M; for X- = CNO-, k2 = 59 M-1 S-1 and k-2 = 0.019 S-1; and for X- = N3-, k2 = 1.6 X 10(2) M-1 S-1 and k-2 = 0.10 S-1. The values of K1K2 from kinetics are in good agreement with those obtained from spectral and [O2] determinations of equilibrated mixtures of Hr, CNO-, and O2. The second step has been analyzed separately by flow observations of the small spectral changes accompanying addition of X- to deoxyhemerythrin. The slower, stoichiometric formation of methemerythrin cyanate or azide has also been studied and second order rate constants for reaction of HrO2 with X- determined (N3-, 0.34 M-1 S-1 and CNO-, 0.08 M-1 S-1 at 25 degrees and pH = 6.3). These are compared with those for accelerated formation of the methemerythrin ligand adduct in the same conditions in presence of NO2- (0.31 M-1 S-1), HCO2- (8.3 X 10(-3) M-1 S-1), F- (0.12 M-1 S-1), Cl- (1.4 X 10(-4) M-1 S-1), and imidazole (4 X 10(-3) M-1 S-1 at pH 8.0). No rapid pre-equilibria are observed in the case of the latter ligands. The effect of pH is examined.

Animals↗
PubMed1977

Different degradation pathways for glucose and fructose in Rhodopseudomonas capsulata.

In Rhodopseudomonas capsulata the enzymes of the Entner-Doudoroff pathway and the Embden-Meyerhof pathway have been examined. Fructose-grown cells contained inducible activities of phosphoenolpyruvate-fructosephospho-transferase and 1-phosphofructokinase and only low levels of fructokinase and 6-phosphofructokinase. Although fructose-grown cells contained, in addition, all the enzymes of the Entner-Doudoroff pathway together with fructose-1,6-diphosphatase and phosphoglucose isomerase, the Entner-Doudoroff pathway was not operative in fructose catabolism and served only the degradation of glucose. The functional separation of glucose and fructose catabolism via the Entner-Doudoroff and a modified Embden-Meyerhof pathway, respectively, was confirmed by different approaches: 1. Radiorespirometric experiments with glucose and fructose labelled in positions 1, 2, 3, 3+4 and 6 have been carried out. The pattern of 14CO2-evolution from position-labelled glucose was characteristic for the Entner-Doudoroff pathway, that from position-labelled fructose for the Embden-Meyerhof pathway. 2. In the presence of arsenite up to 50% of glucose- and fructose-carbon was excreted as pyruvate. Using 1-14C-glucose, 86% of the pyruvate was labelled in the carboxyl group, whereas using 1-14C-fructose only 19% of the pyruvate was labelled in the carboxyl group. 3. A glucose-6-phosphate dehydrogenase-deficient mutant was isolated which lacked a functional Entner-Doudoroff pathway but which was unaltered in its ability to grow on fructose.

Fructose↗
PubMed1976

Diagnostic and therapeutic efficacy of cervical conization.

Cervical conization was perfromed on 756 patients at the University of Kentucky Medical Center from July 1, 1964, to January 1, 1973. Sixty-six patients were pregnant at the time of conization. Eighty-six per cent of patients with cytologic findings of carcinoma in situ had histologic verification of carcinoma in situ or severe dysplasia, and there was absolute correlation between cytology and histology in 75 per cent of patients will occult invasive cancer. Cervical biopsies without colposcopic direction predicted either severe dysplasia or carcinoma in situ in 77 per cent of cases but were accurate in only seven of 24 patients with occult invasive cancer. Carcinoma in situ was present in 30 per cent of hysterectomy specimens following conization but recurred in only seven per cent of patients followed without hysterectomy. Recurrent carcinoma in situ following hysterectomy was more common in patients with residual intraepithelial cancer in the uterus but was independent of the size of the vaginal cuff removed. Major postconization complications requiring hospitalization occurred in 3.4 per cent of nonpregnant patients and in 7.5 per cent of pregnant patients.

Adult↗