Tissue fractionation studies. 5. The association of acid phosphatase with a special class of cytoplasmic granules in rat liver

Abstract

A comparative study was made of the sedimentation properties of bound acid phosphatase and of cytochrome oxidase or the related respiratory activity, in rat-liver fractions. Acid phosphatase sedimented more slowly than did the oxidase. The partial dissociation between the 2 activities, achieved by a single centrifuging, is further enhanced by the use of a layering procedure or by repeated washings. It is concluded that the classical mitochondrial fraction is made up essentially of typical mitochondria, possessing oxidative properties but devoid of acid phosphatase. The latter enzyme is believed to be associated with a special class of granules, very few in proportion, entirely distinct from microsomes, and comparable in size to small mitochondria. In the classical fractionation procedures, these granules are unequally distributed between the mitochondria and the microsomes, occurring mostly in the former fraction. A new scheme of fractionation is described, which will make it possible to distinguish between true mitochondrial enzymes and contaminants of the acid phosphatase type.