Biochemical Balance and Synchronized Cell Cultures

IN cell biochemistry, it is desirable to have criteria for identifying abnormal changes resulting from experimental manipulation, especially during the induction of synchrony. For this purpose, use has been made of the concept of unbalanced growth, first introduced by Cohen and Barner 1 , to explain the death of a thymine-requiring mutant of Escherichia coli as a result of continued cytoplasmic synthesis in the absence of proportional DNA synthesis. Most people who use this concept are doubtless aware that its foundation must be in the biochemical processes within individual cells and that the fundamental definition of “balance” should be at the cellular level. There are, however, examples in the literature in which it is concluded, on the basis of changes in the gross composition of mammalian cell cultures in which the age distribution of cells is changing, that growth is “unbalanced” without proper consideration of the possibility that the changes might result merely from redistribution of individual cells in the several phases of the life cycle, rather than from significant changes in their composition.