1. Lysosome-rich fractions from rat liver were subjected to several disruptive procedures: osmotic lysis or freezing and thawing in different media, shearing forces in a high-speed blender, treatment with Triton X-100. 2. The soluble and particulate phases were then separated by high-speed centrifugation and assayed for their content of acid phosphatase, β-galactosidase, β-N-acetylglucosaminidase, acid proteinase, acid ribonuclease, acid deoxyribonuclease and protein. 3. The degree of elution of these hydrolases appeared to depend on both the enzyme species and the treatment. The resulting patterns of solubilization were rather complex, so that a clear-cut discrimination between soluble and structure-bound enzymes could not always be traced. 4. Although only β-galactosidase was readily solubilizable after all treatments, acid proteinase could also be extensively eluted from the sedimentable material in the presence of EDTA and acid phosphatase was fully extracted by Triton X-100. On the other hand, considerable proportions of the other activities could not be solubilized by any of the procedures used. 5. In other experiments, the adsorbability of hydrolases on subcellular structures was investigated by measuring the partition between sedimentable particles and soluble fraction of solubilized enzymes added to ‘intact’ liver homogenates. 6. Large proportions of acid proteinase, ribonuclease and deoxyribonuclease, and almost all of β-N-acetylglucosaminidase, were found to be adsorbed on the particulate material.

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