Abstract
Potassium of washed liver mitochondria behaves as though contained at a relatively fixed concentration, close to 90 mEq/ liter, in a compartment which includes approximately 1/3 the volume of centrifuged pellets. This compartment may be the membranous substance of the wall and cristae. With kidney mitochondria the amount retained in this way can be increased by 20–50% with initiation of respiration. This effect is inhibited by cyanide and by dinitrophenol; and it has appeared, in studies with radioactive potassium, to be an example of net uptake.