Polyamines in lymphocyte activation

New features of polyamine metabolism have been identified in both the acid-soluble and the acid-insoluble fraction of activated murine splenic lymphocytes. Lymphocytes activated by the B cell mitogen LPS and simultaneously exposed to either 3H-putrescine or /sup 3/H-spermidine show a differential level of metabolism of the two radioactive polyamines. The percent uptake of isotope from the medium is the same for either putrescine or spermidine during the 48 hour activation period. Intracellularly, only 12% of the label take up as putrescine remains as putrescine and the rest is primarily metabolized to spermidine (47%) and spermine (22%). By contrast, 69% of the initial radioactive spermidine remains as spermidine, again a similar percentage is metabolized to spermine (22%), and a small amount appears as putrescine (2.5%). In these studies the authors have demonstrated the presence of two new small radioactive conjugates (5-7%). Radioactive spermidine is 3 times more effective than radioactive putrescine as a precursor of label in acid-insoluble material. Acid-insoluble label derived from putrescine represents 1.8% of the total cell-associated radioactivity whereas that derived from spermidine is 6.0%. HPLC molecular sieving reveals three distinct radioactive macromolecules.