On intracellular oxidation-reduction potential

Abstract

Abstract Two types of oxidations are to be distinguished in living cells; oxidations at the expense of free oxygen, and oxidations at the expense of oxygen derived from complex molecules. The former are what we have named “independent” in contrast to the latter, which are named “coupled” reactions (1). The inde­pendent oxidations may also be called respiratory in nature; they are not utilised as sources of energy except in the special case of homoiothermic animals which are below the point of thermic neutrality. The coupled oxidations are accompanied by reductions which constitute the real syntheses occurring in cells. Only these oxidations are able to compensate for the chemical work represented by the syntheses, as well as the mechanical work derived therefrom. The power of cells to carry out syntheses is thus dependent on the property of certain substances to be oxidised at the expense of oxygen borrowed from complex molecules. In other words, if we admit with Wieland (2) that oxida­tions begin by a mobilisation of hydrogen, the possibility that syntheses may take place depends upon whether the hydrogen is capable of being fixed by an acceptor other than molecular oxygen.