Poly (ADP-ribose) polymerase activity during the growth cycle of mouse fibroblasts (LS cells).

The specific activity of poly (ADP-ribose) polymerase in isolated nuclei of mouse fibroblast cells (LS cells) was estimated throughout the growth cycle. The activity of this enzyme increased approx. 3-fold during the logarithmic phase of the cell population growth and was correlated with the increase in cell number. Upon dilution of the culture, the specific activity dropped, over 12–24 h, approx. 3-fold, to the new low level. This fluctuation in enzyme activity is unlike that of other metabolic enzymes in LS cells. It is not a result of changes in the medium. The specific enzyme activity during the growth cycle is not correlated with the DNA content of the cells. The physiological function of poly (ADP-ribose) polymerase is discussed in relation to these results.