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Added K+ is necessary for maximum rates of respiration and phosphorylation by rat liver mitochondria when a phosphate accepting system such as glucose and hexokinase is present. K+ is also necessary for maximum rates of respiration and phosphorylation when microsomes, or an acetone-soluble fraction therefrom, are present. When respiration is maximally stimulated by 2,4-dinitrophenol, added K+ does not enhance respiration except that in the 3rd and 4th hour of the experiment it prevents deterioration of the mitochondria. It is concluded that K+ participates in transphosphorylation reactions but does not directly influence the oxidative reactions.

The concentration of various anions in the sucrose impermeable space of ratliver mitochondria relative to the applied concentration can be used to calculate an equilibrium potential if one supposes that the anion distribution is passive. Values so calculated for anions of different net charge are about 30 mV, with the interior positive. The relative merits of the hypotheses that an internal positivity is generated by active cation movement or Mitchell 's chemiosmotic generation of an internal negativity coupled with hydroxyl-for-anion exchanges are examined.

Washed, starved preparations of Escherichia coli B metabolize glucose with concomitant uptake of K + and O 2 and extrusion of H + . Abrupt changes in the rates of these processes are correlated with apparent sequential shifting in time of the control sites of aerobic glycolysis from the glyceraldehyde-3-phosphate dehydrogenase-3-phosphoglyceric phosphokinase couple to phosphofructokinase to hexikinase. It is suggested that the principal inhibitors of phosphofructokinase activity are citrate and ATP. The rate of K + uptake is neither a function of the rate of glucose dissimilation nor of the concentration of ATP in these short-term experiments, and the energy available for the active transport of ions appears to vary as the intracellular chemical environment changes.

In previous work a heat-stable, acetone-soluble fraction from rat liver microsomes was found to stimulate the respiration of mitochondria. By means of an assay system based on the activation of latent mitochondrial ATPase, the active component of the microsomal extract has been identified as free fatty acids. Among the saturated fatty acids, myristic exhibited the greatest activity which diminished progressively as the chain was lengthened or shortened. Introduction of a cis unsaturated bond, but not of a trans unsaturation, enhanced activity. During the interaction, the higher fatty acids or DCA are tightly bound by the mitochondria in contrast to DNP which activates latent ATPase without becoming appreciably bound.