The relation of lysosomal enzymes to mammary tumor regression was studied in the highly hormone-dependent MTW9 rat mammary carcinoma. Quantities of the enzymes were determined with the use of a histochemical modification of the single radial immunodiffusion method. Major findings were as follows. (a) Acid phosphatase, arylsulfatase, β-galactosidase, and β-glucuronidase significantly increased in total activities after 48 hr of tumor regression. (b) A marked shift toward free (nonsedimentable) enzyme of each acid hydrolase occurred later in the regression process. (c) Regressing tumors contained larger quantities of β-galactosidase and β-glucuronidase, and the increased amounts closely corresponded to the increments in activities. (d) De novo synthesis of β-galactosidase and β-glucuronidase probably occurred during hormone-dependent tumor regression.

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This is Paper 4 in a series on mammary tumor regression from the Tumor Physiopathology Section, Laboratory of Biochemistry, National Cancer Institute, NIH, Bethesda, Md.

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