FRACTIONATION OF MAMMALIAN LIVER CELLS BY DIFFERENTIAL CENTRIFUGATION : II. EXPERIMENTAL PROCEDURES AND RESULTS.

1. A method is described whereby the major components of liver suspensions are segregated according to size into three main fractions: (a) a large granule fraction composed of elements approximately 0.5 to 2 micro in diameter; (b) a microsome fraction composed of submicroscopic elements approximately 80 to 150 mmicro in diameter; and, (c) a supernate fraction containing the soluble components of the extract. 2. The nature and origin of the constituents of liver extract is discussed. The large granule fraction is deemed to consist mostly of mitochondria and liver secretory granules, whereas the microsome fraction corresponds to the chromophilic ground substance of the hepatic cell. Phosphorus distribution in the supernate fraction, and ultraviolet absorption of the solution suggests that practically all the ribose nucleoproteins of liver extract are sedimentable, and occur in association with the large granules and microsomes. 3. The method of fractionation of liver suspension by differential centrifugation is being used as a means to investigate the chemical constitution of the morphological constituents of cytoplasm, and the distribution of biochemical activities in the cytoplasm of the hepatic cell. 4. The method of differential centrifugation is found to be applicable not only to the fractionation of cells but also, with the aid of auxiliary techniques, to the fractionation of much smaller elements, such as mitochondria.