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With the purpose to clarified the mode of localization and mechanisms of activation of ATPase in the mitochondrial membrane, analyses were made on the properties of mitochondrial ATPase from the structural and functional aspects. The activation of ATPase by DNP and Mg++ and the oligomycin sensitivity were investigated in a series of inner membrane fragment samples obtained by ultrasonic irradiation and those samples obtained in the processes of isolation and purification of ATPase from rat liver mitochondria and beef heart mitochondria in parallel with electron microscope observations. As a result it has been found that the membrane fragments obtained from rat liver and beef heart mitochondria by ultrasonication exhibited high respiratory activity and unmasked ATPase activity which was charac· terized by remarkable stimulation by Mg++ and inhibition by oligomycin and azide. Therefore, mitochondrial ATPase seems to be bound fairly closely to the inner mitochondrial membrane. In the membrane fragments prepared by ultrasonication of intact mitochondria, ATPase activity was stimulated by DNP, but in the supernatant fractions was not. On the other hand, the supernatant fraction obtained from BHM and inner membrane fragments by severe sonication exhibits a marked ATPase activity and the activity incresed in each step of the purification on the treatments with acid, protamine and heat. Especially in the case of membrane fragments the protamine treatment can be omitted. Electron microscope observation of the fractions in each step of the purification proved the head pieces to be ATPase. The ATPase activity of solubilized head pieces is insensitive to oligo. mycin and coincides with the soluble ATPase of PULLMAN etat. (8) in the points of its cold labile property and optimum pH, but it shown no accele. ration of ATPase activity by DNP.

Morphological comparison at colonial level was made on a series of established liver cell lines derived from rats fed 4-dimethylaminoazo-benzene (DAB) for various periods of days for the purpose of elucidating more accurately the differences in morphology and growth patterns among these cell lines. Colonies of each cell line produced by the single cell plating technique were compared with regard to colony size, density and piling-up of cells, atypism and pleomorphism of cells, and the migration of cells from colonies. Plating efficiency of each cell line was also compared. The cultured rat liver cells obtained from those rats fed DAB for a longer period of days showed higher plating efficiency, and increased the incidence of large-sized, dense, and piled-up colonies, of colonies consisted of cells having nuclear atypism and pleomorphism, and of irregularly margined colonies with migrating cells. The correlation between the present results and the process of DABcarcinogenesis is discussed.