Energetics and assimilation in the combustion of carbon compounds by Escherichia coli.

In the preceding paper (Siegel and Clifton, 1950) on the oxidative assimilation of carbohydrates by Escherichia coli considerations of growth, assimilation, and energetics made it evident that free energy relationships alone do not provide conclusive criteria concerning the extent of the assimilability of a carbohydrate utilized by the cell. This has been attributed to the more important role of possible intermediates of the oxidative process that serve as building blocks for the numerous syntheses carried on by the cell. Thus, lactose, with a molar AF for the reaction of oxidative assimilation almost twice that of arabinose or glucose, is assimilated to a lesser extent during growth than the latter two sugars, of which arabinose is more readily assimilated. In the studies to be described this concept has been more exhaustively investigated employing the methods and reasoning previously described (Siegel and Clifton, 1950) and with organic substrates other than sugars.