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Membrane Inlet Mass Spectrometry (membrane + inlet_mass_spectrometry)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

A Comparison of Membrane Inlet Mass Spectrometry and Nitric Oxide (NO) Electrode Techniques to Detect NO in Aqueous Solution

ELECTROANALYSIS, Issue 4 2010
Chingkuang Tu
Abstract The NO electrode and membrane inlet mass spectrometry (MIMS) have the advantage of being sensitive, direct, and real time detectors of NO in aqueous solution. They do not require reacting NO with labels or purging of NO with an inert gas. We show that the NO electrode and MIMS are comparable in sensitivity detecting NO concentrations to 0.5,nM in aqueous solution, and both give identical results in a biological measurement, the reactions of deoxyhemoglobin with nitrite. [source]

Light-dependent oxygen consumption in nitrogen-fixing cyanobacteria plays a key role in nitrogenase protection,

JOURNAL OF PHYCOLOGY, Issue 5 2007
Allen J. Milligan
All colonial diazotrophic cyanobacteria are capable of simultaneously evolving O2 through oxygenic photosynthesis and fixing nitrogen via nitrogenase. Since nitrogenase is irreversibly inactivated by O2, accommodation of the two metabolic pathways has led to biochemical and/or structural adaptations that protect the enzyme from O2. In some species, differentiated cells (heterocysts) are produced within the filaments. PSII is absent in the heterocysts, while PSI activity is maintained. In other, nonheterocystous species, however, a "division of labor" occurs whereby individual cells within a colony appear to ephemerally fix nitrogen while others evolve oxygen. Using membrane inlet mass spectrometry (MIMS) in conjunction with tracer 18O2 and inhibitors of photosynthetic and respiratory electron transport, we examined the light dependence of O2 consumption in Trichodesmium sp. IMS 101, a nonheterocystous, colonial cyanobacterium, and Anabaena flos-aquae (Lyngb.) Bréb. ex Bornet et Flahault, a heterocystous species. Our results indicate that in both species, intracellular O2 concentrations are maintained at low levels by the light-dependent reduction of oxygen via the Mehler reaction. In N2 -fixing Trichodesmium colonies, Mehler activity can consume ,75% of gross O2 production, while in Trichodesmium utilizing nitrate, Mehler activity declines and consumes ,10% of gross O2 production. Moreover, evidence for the coupling between N2 fixation and Mehler activity was observed in purified heterocysts of Anabaena, where light accelerated O2 consumption by 3-fold. Our results suggest that a major role for PSI in N2 -fixing cyanobacteria is to effectively act as a photon-catalyzed oxidase, consuming O2 through pseudocyclic electron transport while simultaneously supplying ATP in both heterocystous and nonheterocystous taxa. [source]

Simultaneous determination of Rubisco carboxylase and oxygenase kinetic parameters in Triticum aestivum and Zea mays using membrane inlet mass spectrometry

PLANT CELL & ENVIRONMENT, Issue 3 2010
A. B. COUSINS
ABSTRACT The lack of complete Rubisco kinetic data for numerous species is partly because of the time consuming nature of the multiple methods needed to assay all of the Rubisco parameters. We have developed a membrane inlet mass spectrometer method that simultaneously determines the rate of Rubisco carboxylation (vc) and oxygenation (vo), and the CO2 and O2 concentrations. Using the collected data, the Michaels-Menten equations for vc and vo in response to changing CO2 and O2 concentrations were simultaneously solved for the CO2 (Kc) and O2 (Ko) constants, the maximum turnover rates of the enzyme for CO2 (kcatCO2) and O2 (kcatO2) and the specificity for CO2 relative to O2 (Sc/o). In the C4 species Zea mays Kc was higher but Ko was lower compared with the C3 species Triticum aestivum. The kcatCO2 was higher and the kcatO2 lower in Z. mays compared with T. aestivum and Sc/o was similar in the two species. The Vomax/Vcmax was lower in Z. mays and thus did not correlate with changes in Sc/o. In conclusion, this mass spectrometer system provides a means of simultaneously determining the important Rubisco kinetic parameters, Kc, Ko, kcatCO2,kcatO2 and Sc/o from the same set of assays. [source]