An alternate method of calculating the heat of growth of Escherichia coli K‐12 on succinic acid

Abstract

The ΔH unit weight of a complex substance such as a biological macromolecule is almost always obtained by means of combustion analysis. In theory, this can also be done by summing the ΔH values for the monomers comprising the macromolecule plus the enthalpic energies involved in their polymerization. The enthalpy of formation of one unit‐carbon formula weight of dried Escherichia coli K‐12 cells was determined by summing the values of the enthalpies of formation of the quantities of monomers in the major classes of macromolecules substances comprising the cellular biomass and the enthalpic energies involved in their polymerizations. To this value was added the enthalpy of formation of the cellular ions in their aqueous standard states, per unit‐carbon formula weight of cellular substance and the enthalpy change with respect to the ionization of the protein amino acid side chains. If it is assumed that the cellular fabric is insoluble and that the ions are soluble, the sum of the enthalpies of formation of all the cellular components should closely approximate the enthalpy of formation of one unit‐carbon formula weight equivalent of living cells. Using this value, a calculation of the enthalpy change accompanying anabolism shows this latter to be effectively zero, indicating that the heat of growth (anabolism plus catabolism) is equal to that calculated for catabolism alone. This conclusion is in accord with those of several investigators who have used manometry or direct calorimetry.