Polarographic studies of energy metabolism in rat liver homogenates

¹ Physiology Laboratories, Department of Zoology, Pennsylvania State University, University Park, Pennsylvania and Bio-Chemistry Division, U. S. Army Medical Research Laboratory, Fort Knox, Kentucky

Oxidative phosphorylation and respiratory regulation were studied in rat liver homogenates by use of the oxygen electrode. Addition of 250 µm ADP to rat liver homogenates containing succinate, -ketoglutarate, ß-hydroxybutyrate, or glutamate stimulated respiration 300–600%. Respiration declined sharply after the added ADP was phosphorylated. ATP, especially in the presence of MgCl₂, also stimulated homogenate respiration, though much less effectively than ADP at equivalent concentrations below 1 mm. Amytal or malonate, in concentrations sufficient to depress substrate-ADP respiration, had no effect on substrate-ATP respiration. ADP:O ratios were measured and corrected for ATPase activity. Values obtained were 2.0, 4.1, and 3.0 for succinate, -ketoglutarate, and ß-hydroxybutyrate, respectively.