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M Ortner

Publications and source records attributed to M Ortner.

20 records · Page 2Linked to original sources
PubMed1994

A respirometer for investigating oxidative cell metabolism: toward optimization of respiratory studies.

Oxygen flux measurements are critical at low rates of. respiration and at oxygen tensions below air saturation. Difficulties are primarily due to increased oxygen diffusion and consumption processes which may occur in conventional closed respirometric chambers. To avoid measurement errors encountered with standard equipment, a new type of oxygraph was developed. This instrument provides reliable quantification of oxygen flux in small organisms, tissue samples, cells, isolated mitochondria, and chloroplasts. The instrument is available commercially or can be rebuilt in a well-equipped laboratory workshop.

Cells↗
PubMed1991

Reversibility of oxygen switch-off effect on Bacillus polymyxa nitrogenase.

The objective of this study was to analyse in vivo the effect of oxygen on the nitrogenase of Bacillus polymyxa. The culture technique employed in this study prevented spore formation by B. polymyxa during the entire period of exposure to acetylene. Under these conditions the acetylene-reduction assay allowed quantification of nitrogenase activity over long incubation periods (44 h). Nitrogenase activity was highest in cells harvested in the late logarithmic phase. At PO2 of 0.19 and 0.37 kPa, acetylene reduction was inhibited by 80 and 100%, respectively. This switch-off effect could be reversed through oxygen exhaustion, either by flushing the culture with N2 or by cellular respiration, suggesting a respiratory protection mechanism for the nitrogenase complex in B. polymyxa. Oxygen consumption measured by a closed-chamber respirometer showed a linear increase up to a PO2 of 0.2 kPa. Above 0.3 kPa a saturation in oxygen consumption was observed. Exposure to high oxygen pressures resulted in an irreversible loss of nitrogenase activity. The oxygen inhibition pattern was shown to be similar to that in other microaerophilic and anaerobic nitrogen-fixing microorganisms.

Bacillus↗