Glycolytic enzyme activities in malignant cells grown in vitro and in vivo.

Cell proximity has a profound effect on the glycolytic enzyme levels observed in mammalian cells grown in vitro. Hexokinase activity generally increased with the increasing cell density of both untransformed and virus-transformed cultures. In contrast, phosphofructokinase and pyruvate kinase activities were generally elevated only in crowded cultures of transformed cells. A spontaneous experimental mouse tumor cell line (EMT6) exhibited cell crowding-dependent elevations in glycolytic enzyme levels when cultured in vitro. The glycolytic enzyme levels of experimental mouse tumors grown in vivo, on the other hand, were constant and normally less than those observed in cultured EMT6 cells.