The sources of thermal energy exchange accompanying microbial catabolism.
Calculations are made of thermal energy exchanges from catabolic reactions in the aqueous state, using thermodynamic properties at 0.001 M, indicated by subscript "(B)". Heats of reaction are calculated as DeltarHB,298.15o'=DeltarXB,298.15o'+DeltarQab,B,298.15o' (1), or as DeltarHB,298.15o'=DeltarGB,298.15o'+TDeltarSB,298.15o' (2), where DeltarXo'B,298.15 and DeltarGo'B,298.15 represent non-thermal, chemical energy converted into thermal energy during a reaction and where DeltarQab,B,298.15o'andTDeltarSB,298.15o' represent the exchange of absorbed thermal energy as reactants become converted into products. Percentages are tabulated of the thermal energy exchanges contributed to DeltarHB,298.15o' by DeltarXB,298.15o' and DeltarQab,B,298.15o', and by DeltarGB,298.15o' and TDeltarSB,298.15o'. Aerobically, for substrates not containing nitrogen, the value of DeltarXB,298.15o' averages 4.21% more negative than that of DeltarGB,298.15o'. For substrates containing nitrogen this average drops to 1.80%. For substances not containing nitrogen, the thermal energy contributed by DeltarQab,B,298.15o' to DeltarHB,298.15o' averages 2.21%, whereas that contributed by TDeltarSB,298.15o' averages -1.95%. The difference is 4.16%, which is close to the average value of 4.21% that DeltarXB,298.15o' is more negative than DeltarGB,298.15o'. This observation indicates that the difference between DeltarXB,298.15o' and DeltarGB,298.15o' is due almost entirely to the manner in which exchanges in absorbed thermal energies are measured or calculated for the reaction systems studied. The same applies to the oxidation of substances containing nitrogen. Here, the thermal energy contributed to DeltarHB,298.15o' by DeltarQab,B,298.15o' averages 5.32%, whereas that contributed by TDeltarSB,298.15o' averages 3.50%. The difference between them is 1.82%, which is close to the average value of 1.80% that DeltarXB,298.15o' is more negative than DeltarGB,298.15o'. Anaerobically, for the processes tested fewer inferences could be drawn. The values of DeltarGB,298.15o' are much more negative than those of DeltarXB,298.15o' in three examples out of five and widely variable, quite the opposite of the data on the aerobic processes. One anaerobic DeltarXB,298.15o' value is positive, indicating that something other than the total free energy change must be driving this particular process.
Battley
Edwin H
EH
Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY 11794-5245, USA. battley@life.bio.sunysb.edu
D001419:Bacteria / Q000378:metabolism*; D004734:Energy Metabolism; D008954:Models, Biological; D013816:Thermodynamics