Polyamine content of AKR leukemic cells in relation to the cell cycle.

Summary In AKR mice that develop spontaneous lymphoid leukemia, the thymus is the organ of primary involvement. Thymic cells from normal mice, as well as from mice with advanced leukemia, were separated according to size by sedimentation in a 1 × g sucrose gradient, the larger cells sedimenting further than the smaller cells. The fractions obtained from this gradient, which correspond to successive phases of the cell cycle, were collected and subjected to polyamine analysis. In the G0 phase of the cell cycle the spermine content was higher than in the G1 phase, whereas the putrescine and spermidine content were similar in these two phases. The cellular content of putrescine, spermidine, and spermine increased progressively as the cells traversed the cell cycle from G1 to M. In fact, the amount of all these amines was increased in the G1 + S fraction. In the fraction corresponding to the G2 + M phases, the polyamine content was twofold that in the G1 phase. This increase in the polyamine content was seen first for putrescine, then for spermidine, and finally for spermine. This sequential pattern reflects the order of synthesis of the polyamines, i.e., putrescine being the precursor of spermidine and spermidine the precursor of spermine.