The rates of incorporation of uniformly labeled l-leucine-14C into protein and of choline-methyl-14C and l-methionine-methyl-14C into the phosphatidylcholine of the organelle membranes was determined for tissue slices prepared from normal mammary glands, preneoplastic hyperplastic alveolar nodule outgrowths, and mammary adenocarcinomas of C3H mice. The relative incorporation rates of uniformly labeled leucine-14C and of choline-methyl-14C were compared with the rate of incorporation of thymidine-methyl-3H into the DNA of each tissue. The rate of membrane protein synthesis as indicated by the leucine incorporation rate did not correlate with cell growth, since synthesis in the rapidly growing mammary glands in pregnant mice was not significantly greater than that in the slower growing mammary glands in lactating mice. The observations were made that methylation of phosphatidylethanolamine did not contribute to phosphatidylcholine synthesis and that the correlation between choline-methyl-14C and thymidine-methyl-3H incorporation in the various mammary gland tissues was good. These findings suggest that choline incorporation into phosphatidylcholine has general applicability to studies on membrane proliferation in mammary glands.

Subcellular fractions from each mammary tissue were assayed for activities of phosphodiesterase I and NADPH-cytochrome c reductase enzymes localized in the endoplasmic reticulum. NADPH-cytochrome c activity in the hyperplastic alveolar nodule outgrowth was similar to that in normal lactating gland rather than that in the histologically identical normal gland of pregnancy. The intracellular distribution of NADPH-cytochrome c activity in the mammary adenocarcinoma suggests that homogenization of this tumor produces particles, derived from the endoplasmic reticulum, with a density distribution different than that produced from normal tissue.

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This investigation was supported by USPHS Research Grants CA-10971 and CA-11736 from the National Cancer Institute and by General Research Support Grant RR-05733.

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