Cyclic 3',5'-nucleotide phosphodiesterases of Novikoff rat hepatoma, mouse L, and HeLa cells growing in suspension culture.

(1 to 7 mM). For cell extracts from all 3 cell lines, specific activities for the low-K^ phosphodiesterase are similar, although there is slightly higher activity in extracts of the fastest-growing Novikoff cells than in extracts from the other cell lines. In contrast, the specific activity for the high-Km phosphodiesterase is 30 to 40 times higher in L than in Novikoff cell extracts and intermediate in HeLa cell extracts, and in Novikoff cells there is only 5 to 10% as much activity as in rat liver. The specific activities for the 2 phosphodiesterases do not change significantly during the growth cycle in suspension culture.