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Biomedical subjects

A G Miller

Publications and source records attributed to A G Miller.

At least 55 records · Page 3Linked to original sources
PubMed1980

Evidence for HCO(3) Transport by the Blue-Green Alga (Cyanobacterium) Coccochloris peniocystis.

The possibility of HCO(3) (-) transport in the blue-green alga (cyanobacterium) Coccochloris peniocystis has been investigated. Coccochloris photosynthesized most rapidly in the pH range 8 to 10, where most of the inorganic C exists as HCO(3) (-). If photosynthesis used only CO(2) from the external solution the rate of photosynthesis would be limited by the rate of HCO(3) (-) dehydration to CO(2). Observed rates of photosynthesis at alkaline pH were as much as 48-fold higher than could be supported by spontaneous dehydration of HCO(3) (-) in the external solution. Assays for extracellular carbonic anhydrase were negative. The evidence strongly suggests that HCO(3) (-) was a direct C source for photosynthesis.Weakly buffered solutions became alkaline during photosynthesis with a one-to-one stoichiometry between OH(-) appearance in the medium and HCO(3) (-) initially added. Alkalization occurred only during photosynthesis and was blocked by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea, diuron. It is suggested that HCO(3) (-) was transported into cells of Coccochloris in exchange for OH(-) produced as a result of HCO(3) (-) fixation in photosynthesis.The inorganic C concentration required to support a rate of photosynthesis of half the maximum rate (K(m)) was 6 micromolar at pH 8.0 or, in terms of available CO(2), a K(m) of 0.16 micromolar. This value is two orders of magnitude lower than reported K(m) values for the d-ribulose-1,5-bisphosphate carboxylase for blue-green algae. It is suggested that the putative HCO(3) (-) transport by Coccochloris serves to raise the CO(2) concentration around the carboxylase to levels high enough for effective fixation.

Journal Article↗
PubMed1980

Active transport and accumulation of bicarbonate by a unicellular cyanobacterium.

The rates of inorganic carbon accumulation and carbon fixation in light by the unicellular cyanobacterim Coccohloris peniocystis have been determined. Cells incubated in the light in medium containing H14CO3- were rapidly separated from the medium by centrifugation through silicone oil into a strongly basic terminating solution. Samples of these inactivated cells were assayed to determine total 14C accumulation, and acid-treated samples were assayed to determine 14C fixation. The rate of transport of inorganic into illuminated cells was faster than the rate of CO2 production in the medium from HCO3- dehydration. This evidence for HCO3- transport in these cells is in agreement with our previous results based upon measurements of photosynthetic O2 evolution. A substantial pool of inorganic carbon was bulit up within the cells presumably as HCO3- before the onset of the maximum rate of photosynthesis. Large accumulation ratios were observed, greater than 1,000 times the external HCO3- concentration. Accumulation did not occur in the dark and was greatly suppressed by the photosynthesis inhibitors 3-(3,4-dichlorophenyl)-1,1-dimethyl urea and 3-chloro-carbonylcyanide phenylhydrazone. These results indicate that the accumulation of inorganic carbon in these cells involves a light-dependent active transport process.

Bicarbonates↗
PubMed1977

The effects of crystal size distributions on the crystallinity analysis of bone mineral.

The mechanisms by which crystal size distributions affect the usual method of quantities X-ray diffraction analysis of bone mineral have been determined on synthetic crystals. It was observed that each component of a crystal-size distribution diffracts independently. This independence causes systematic nonlinear behavior in the plot of integrated intensity vs. broadening parameter curves. The nonlinearity resulted in an overestimation of the amount of nondiffracting material present in bone mineral. Because crystal size distributions may vary for different crystallographic directions, it is strongly suggested that the usual practice of adding the c-axis and a-axis integrated intensities to estimate the crystallinity of the sample be discontinued. Methods of understanding the crystal size distribution function in bone mineral are discussed and evaluated.

Bone and Bones↗
PubMed1977

Precise measurement of total body water using trace quantities of deuterium oxide.

This study was undertaken to investigate the possibility of measuring total body water in human subjects to better than +/-0.5%. Accurate serial estimates of total body water were required to complement densitometric and anthropometric measurements used to monitor body compositional changes in obese patients undergoing dietary or surgical weight reduction therapy. The method required the oral administration of 1-2 g of deuterium oxide and the analysis of pre-dose and respective equilibrated samples of urine, plasma or saliva. The sample size required for analysis was 5 microliter and the conversion of gaseous phase was accomplished using a uranium reduction furnace. Isotopic enrichment of samples was measured using a mass spectrometer incorporating several features designed to cope with problems inherent in H2/H2H isotopic analysis. Reproducibility of sample preparation and accuracy of the mass spectrometer were tested using international standards and shown to give an overall sensitivity of 2 parts in 10(7) for the determination of deuterium in H2O/H2HO mixtures. This precision has enabled us to demonstrate that isotopic fractionation of deuterium with respect to hydrogen occurs within the body and expands the potential use of this isotope for quantitative biochemical studies in the human subject.

Body Water↗
PubMed1977

Measurement of the Cytoplasmic pH in Nitella translucens: Comparison of Values Obtained by Microelectrode and Weak Acid Methods.

A comparison has been made between the use of two types of pH microelectrode and the weak acid method for determining the cytoplasmic pH of Nitella translucens at an external pH of 6. There was good agreement between the value obtained with glass pH microelectrodes (7.54 +/- 0.15 se) and that obtained using the weak acid 5,5-dimethyloxazolidine-2,4-dione (7.42 +/- 0.07 se). Plastic-insulated antimony microelectrodes gave a significantly lower value (6.74 +/- 0.15 se) possibly due to disruption of the insulation by the cell wall. The addition of 1 mM NaN(3) rapidly reduced the pH recorded by the glass pH microelectrodes to about 5.3. A smaller change was observed using the weak acid method. The relevance of this observation to recent work on indoleacetic acid transport is discussed.

Journal Article↗
PubMed1976

Influence of exogenous sugars and polyols on C1-influx and efflux by the ascomycete Neocosmospora vasinfecta.

Glucose and other transportable sugars and polyols inhibited Cl- influx very soon after addition to mycelium in the process of Cl- accumulation. Under the usual experimental conditions (0.1 mM KCl, glucose greater than or equal to 2 mM) the mean percentage of inhibition of Cl- influx by glucose was 54.1 +/- 8.0 (+/- standard error; N = 26). Transport of the exogenous carbohydrate was necessary for inhibition of Cl- influx. Thus, the estimated Ki for glucose inhibition of Cl- influx (28 muM) was close to the Km for glucose transport; glycerol did not inhibit Cl- influx unless it was itself transported, and the degree of inhibition exerted by various carbohydrates correlated with their uptake rates. Inhibition was not caused by the accumulated sugar itself, as high levels (ca. 60 mM) of intramycelial 3-O-methylglucose gave rise to a stimulation of Cl- influx when the exogenous sugar was removed. It is suggested that interaction of Cl- and carbohydrate transport arises from competition for a common energy-coupling mechanism in the cell membrane. Both glucose and 3-O-methylglucose elicited Cl- efflux, but the maximal Cl- efflux rates were observed only after 40 min of incubation and only in the presence of the readily metabolizable glucose. Removal of the exogenous glucose, even after maximal Cl- efflux had been established, resulted in the rapid cessation of efflux. Studies under anaerobic conditions gave further evidence that glucose uptake was necessary and that efflux was not due to temporary depletion of energy reserves. It is proposed that glucose-induced leakage of Cl- is due to reversal of the Cl- uptake system, even though the Km for efflux is much greater than that for influx.

Alcohols↗
PubMed1976

Evidence for a negative membrane potential and for movement of C1- against its electrochemical gradient in the ascomycete Neocosmospora vasinfecta.

The iodides of three lipid-soluble cations (dibenzyldimethylammonium; tribenzylmethylammonium, TBMA+; ethyldimethylbenzylammonium) were synthesized by the reaction of 14C-labeled methyl or 14C-labeled ethyl iodide with the appropriate secondary of tertiary amine and used in an attempt to measure the transmembrane electrical potential difference in Neocosmospora. Only mycelium containing high levels of Na+ accumulated measureable amounts of these cations and only above pH 6. Uptake was reduced in the presence of exogenous K+, Na+, Mg2+, or tris(hydroxymethyl)aminomethane. The velocity of TBMA+ uptake was proportional to its concentration between 46 and 427 muM. Neither the rate nor the extent of TBMB+ uptake was greatly affected by the presence of a fivefold excess of either dibenzyldimethylammonium or ethyldimethylbenzylammonium, even though these cations were themselves accumulated. The uncoupler m-chlorophenylhydrazone induced loss of previously accumulated TBMA+ from the mycelium. Anaerobiosis and cold (5 degrees C) temperature both inhibited TBMA+ uptake but did not induce the loss of previously accumulated TBMA+. The uptake of lipophilic cations by Na+-rich mycelium indicated a minimum transmembrane electrical potential of -60 to -70 mV (inside negative). Net uptake of these cations appeared to be strongly influenced by the availability of endogenous exchangeable cations and by the presence of other exogenous cations, as well as by the membrane potential. Despite these limitations, transport of C1- by Na+-rich mycelium appeared to take place against the electrochemical gradient for C1-.

Anaerobiosis↗
PubMed1975

Halide uptake by the filamentous ascomycete Neocosmospora vasinfecta.

The uptake of Cl minus by the ascomycetes Neocosmospora vasinfecta was investigated. Intramycelial concentrations of more than 55 mM (890-fold the external concentration) were reached. Accumulation was as inorganic Cl minus and nystatin induced total loss of mycelial Cl minus without extensive protein loss, implying that Cl minus retention was not due to binding to macromolecules. Cl minus transport was largely unidirectional with efflux being low under all conditions. Uptake was temperature dependent (maximal Arrhenius activation energy of 18.0 kcal/mol) and was severely reduced by KCN, dicyclohexylcarbodiimide, and anaerobiosis. A comparison with the inhibition of oxygen uptake under the same conditions implied that Cl minus transport was not directly coupled to aerobic electron transport. Cl minus uptake was a saturatable function of the external Cl minus concentration, and apparent Km values of 6.4 times 10-6 M and 10-4 M were calculated. Of the anions tested, only Br minus effectively inhibited Cl minus uptake and I minus, NO3 minus, SO4 minus 2, HCO3 minus, and H2PO4 minus were without effect. Cl minus uptake did not require concomitant cation uptake.

Anaerobiosis↗
PubMed1975

The development of an increased rate of Cl- uptake in the ascomycete Neocosmospora vasinfecta.

Freshly harvested mycelium of the filamentous ascomycete Neocosmospora vasinfecta accumulated C1- against a concentration gradient by a process probably requiring the expenditure of metabolic energy. When mycelium, washed free of growth medium, was incubated in deionized water or tris (hydroxymethyl) aminomethane sulfate at pH 7.5 for 4 h and then transferred to K36C1 solutions, the C1- uptake rate was, on the average, 3.77 +/- 0.26 (+/-SE, N = 20) times the uptake rate exhibited by freshly harvested mycelium. This development of an increased rate of Cl- uptake could be blocked by the presence of an inhibitor of ribonucleic acid synthesis (azaguanine) or of protein synthesis (cycloheximide, fluorophenylalanine, or puromycin). The combined presence of glucose and a potassium salt in the preincubation solution virtually arrested the development of enhanced Cl- uptake. The rate of Cl- uptake by freshly harvested mycelium did not vary greatly with the age of the culture on harvest but the ability to develop an increased rate declined with age. The fact that it is possible to obtain mycelium possessing widely different capacities for Cl- uptake should assist in biochemical characterization of the Cl- uptake system.

Azaguanine↗
PubMed1974

A study of the control of glycolate excretion in chlorella.

Chlorella pyrenoidosa cells grown on 5% CO(2) excreted glycolate when incubated in light with 10 mm bicarbonate, but excreted no glycolate under the same conditions when they were maintained on air for 7 hours prior to the assay. Incubation of 5% CO(2)-grown and air-grown cells with 10 mm isonicotinyl hydrazide or 10 mm alpha-hydroxypyridinemethane sulfonate during the assay stimulated the excretion of glycolate by CO(2)-grown cells severalfold that of air-grown cells.Adaptation of CO(2)-grown Chlorella to growth on air did not affect the levels of glycolate dehydrogenase in the cells and did not affect the rate of dark oxidation and metabolism of exogeneous (14)C-glycolate by the cells. These results indicate that the lack of glycolate excretion by air-grown or air-adapted cells of Chlorella cannot be explained by a concomitant change in the level of glycolate dehydrogenase.

Journal Article↗