The subcellular distribution of twelve acid hydrolases was studied in rat lung homogenates. The distribution profile of all the hydrolases, except cathepsin C (EC 188.8.131.52), is similar to that of lysosomal enzymes in rat and guinea pig liver. The microsomal marker, glucose-6-phosphatase (D-glucose-6-phosphate phosphohydrolase, EC 184.108.40.206), and mitochondrial marker, the succinate oxidase system, were localized mainly in their respective fractions. The increases of specific activities of the light-mitochondrial fraction over the homogenate specific activities are similar to those obtained for rat liver and indicates the usefulness of the differential centrifugation method described for preparation of acid hydrolase-rich fractions from lung homogenates. This study also shows some qualitative similarities in the hydrolase complements of lung and liver.
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