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Abstract
The Arrhenius activation energies, and therefore temperature coefficients, for rates of catabolic production of ATP and for anabolic use of ATP differ. Because the intracellular concentration of ATP and the phosphorylation potential must be controlled within a narrow range for cell survival, a mechanism must exist to balance these rates during temperature variation in ectotherms. We hypothesize that much of this control is accomplished via engagement of temperature-dependent reactions that waste ATP or the potential to make ATP in "futile" cycles and that energy-wasting metabolic cycles are essential for maintaining acceptable phosphorylation potentials across a temperature range. We further postulate that the mitochondrial alternative oxidase (AOX) activity is one important mechanism for "wasting" potential to make ATP and thus for controlling the phosphorylation potential in plants as temperature or other reaction conditions vary. Because of differences in temperature coefficients, the ratio of AOX to COX activities varies with temperature, resulting in a temperature-dependent change in coupling oxidation to phosphorylation. Matching the changes in substrate carbon conversion efficiency to environmental temperature patterns allows plants to maintain constant phosphorylation potentials. Thus, an apparent paradox exists that survival of all organisms in changing conditions depends on an energy loss via "futile cycles."
Parent Publication
Citation
Hansen, Lee D.; Smith, Bruce N.; Criddle, Richard S.; Church, J. N. 2001. Responses of plant growth and metabolism to environmental variables predicted from laboratory measurements. In: McArthur, E. Durant; Fairbanks, Daniel J., comps. Shrubland ecosystem genetics and biodiversity: proceedings; 2000 June 13-15; Provo, UT. Proc. RMRS-P-21. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 259-264.
