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The two calorespirometric ratios, the ratio of metabolic heat rate to the rate of CO2 production and the ratio of metabolic heat rate to the rate of O2 uptake (Rq/ R C O 2 and Rq/ R O 2 , respectively), provide different information about the activities of metabolic pathways. In a steady state system, Rq/ R C O 2 depends only on the oxidation state of the substrate and Rq/ R O 2 equals Thornton's constant or the oxycaloric equivalent. In a growing or developing system, the measured ratio Rq/ R O 2 differs from the oxycaloric equivalent only if reactions that do not consume oxygen and have nonzero ΔH are present. Relative rates of aerobic and anaerobic (with ΔH ≠ 0) reactions can thus be calculated from the measured Rq/ R O 2 , but the substrate carbon conversion efficiency cannot. The difference between the Rq/ R C O 2 ratio predicted from Thornton's rule and the actual measured ratio contains information on the rates of anaerobic reactions with ΔH ≈ 0. The latter ratio thus allows partitioning of the CO2 production rate between oxidative catabolism and anabolic reactions with ΔH ≈ 0. This partitioning allows calculation of substrate carbon conversion efficiency and rates of growth or development. |
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