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Cyclic 3',5'-Nucleotide Phosphodiesterases of Novikoff Rat Hepatoma, Mouse L, and HeLa Cells Growing in Suspension Culture¹

Department of Microbiology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, and the Division of Research, National Jewish Hospital and Research Center, Denver, Colorado 80206

Cultured Novikoff rat hepatoma, human HeLa, and mouse L cells contain 2 cyclic 3',5'-nucleotide phosphodiesterases, 1 with a low apparent K_m of 1 to 2 M for cyclic 3',5'-monophosphate and another with an apparent K_m of 100 to 400 M. The high-K_m phosphodiesterases are inhibited by theophylline in a simple, competitive manner, whereas the low-K_m enzymes are inhibited in a noncompetitive manner, although the K_i's of inhibition are similar for both activities (1 to 7 mM). For cell extracts from all 3 cell lines, specific activities for the low-K_m 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-K_m 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.

¹ Supported by USPHS Research Grant AI 07250 from the National Institute of Allergy and Infectious Diseases.

Received 12/20/71. Accepted 2/16/72.