Oxygen concentration at which respiratory system still generates close to maximal pmf (proton motif force)

Value 10 % of normal levels (i.e. 20%/10) Range: 2% (in air) = 24 µM O2 = 1 ppm (in liquid) % of normal levels (i.e. 20%/10)
Organism Bacteria Escherichia coli
Reference Walter JM, Greenfield D, Bustamante C, Liphardt J. Light-powering Escherichia coli with proteorhodopsin. Proc Natl Acad Sci U S A. 2007 Feb 13 104(7):2408-12. p.2409 right column 2nd paragraphPubMed ID17277079
Primary Source Setty OH, Hendler RW, Shrager RI. Simultaneous measurements of proton motive force, delta pH, membrane potential, and H+/O ratios in intact Escherichia coli. Biophys J. 1983 Sep43(3):371-81. p.377 left column bottom paragraphPubMed ID6354293
Method "To test the possibility that light-driven proton pumping is most beneficial to aerobically grown cells when their ability to respire is suddenly impaired, [researchers] energy-depleted the cells. Because E. coli is difficult to energy-deplete by nutrient limitation because of its endogenous energy stores (20, 21), [researchers] additionally used the respiratory poison azide, which has multiple cellular effects (22, 23) but primarily inhibits cytochrome oxidase and, thus, proton extrusion by the respiratory chain, stopping the flagellar motor (18)."
Comments To convert from units of ngA oxygen/ml stated below to uM divide by 2. "Reduced proton pumping by the respiratory system causes the pmf [proton motif force] to drop. Light-based proton pumping by proteorhodopsin can then increase the pmf. Removal of oxygen from the cell culture also should lead to light-responsive bacteria with none of the possible confounding effects of azide. [Researchers] needed to reduce O2 levels substantially, because at 0.3 ppm, the E. coli respiratory system still generates ˜50% of the normal pmf (primary source)." Primary source p.377 left column bottom paragraph:"Fig,6 shows the magnitudes of PMF, ?? [membrane potential], and ?pH developed in response to different amounts of oxygen used to support respiration. As little as 14 ngA [nanogram atoms] of oxygen per milliliter, which represents 3% of the concentration of oxygen in air-saturated buffer at room temperature, caused the formation of ~50% of the maximum PMF and ~65% of maximal ??. Near maximal levels for PMF, ??, and ?pH were attained with 47.5 ngA/ml of oxygen, which still is only 10% of the air-saturated concentration."
Entered by Ron Milo - Admin
ID 111098