Abstract
Dog cerebrum was homogenized in 0.25M sucrose and fractionated by differential centrifugation to yield a "nuclear" sediment, three cytoplasmic particulate fractions and the final supernate. Each of these fractions was found to contain acid and alkaline phosphatase, 5'-nucleotidase, and pyrophosphatase activity. With the exception of alkaline phosphatase, the nuclear fraction contains very little enzyme activity, which may be due to cytoplasmic contaminants. The high alkaline phosphatase activity of the nuclear fraction originates from components other than the cell nuclei. The cytoplasmic particles contain a low percentage of the total alkaline phosphatase and pyrophosphatase activities, but relatively more of the acid phosphatase and 5' nucleotidase. The final supernate contains almost all of the pyrophosphatase activity. The specific activity of the three phosphomonoesterases in the supernate is low. The localization of the Nissl substance in the cytoplasmic particulate fractions is discussed.