Mouse mammary cells in D-valine medium.

Cells of a mouse mammary epithelial cell line as well as fibroblasts from a mouse mammary explant were severely inhibited from proliferating in a medium in which D-valine was substituted for L-valine. After the first few days in D-valine medium, the number of epithelial cells did not increase despite the fact that a few percent continued to synthesize DNA. The cells did recognize the presence of the D-valine in the medium because cells in D-valine increased in volume and their numbers remained stationary, whereas cells without valine shrank and the cell numbers decreased with time.