The relationship of cAMP levels and the rate of pool labelling of cAMP and related bases, nucleosides and nucleotides to the HeLa cell cycle. |
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Authors: | A A Al-Bader P N Rao A Orengo |
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Institution: | Departments of Developmental Therapeutics and Biochemistry, The University of Texas System Cancer Center, M. D. Anderson Hospital and Tumor Institute, Houston, TX 77030, USA |
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Abstract: | Cellular cAMP levels as well as the rate of pool labelling of cAMP and related bases, nucleosides and nucleotides were determined in synchronized cultures of HeLa cells after pulse-labelling with 14C]adenine. The cAMP levels were found to be maximal in G 1 and minimal in G 2 and mitosis, as previously reported by others. The rate of labelling of the cAMP pools, however, was found to be maximal in G 2 and decreased to a minimum in G 1. This suggests that the rate of cAMP synthesis is highest when pool level is lowest and vice versa. A comparison of cAMP levels and the rate of 5′AMP pool labelling throughout the HeLa cell cycle indicated an inverse relationship. Such a relationship emphasizes the role of the cyclic 3′,5′-phosphodiesterase activity during the cell cycle. The kinetics of pool labelling of IMP, ATP, and hypoxanthine throughout the cell cycle suggested that the adenylate energy charge fluctuated as a function of the cell cycle. The apparent activation of the adenylate cyclase during G 2 and mitosis as reflected by the increased rate of cAMP pool labelling suggests that the super phosphorylation of H 1 histone during G 2-mitotic transition may be mediated by cAMP-dependent phosphokinases. |
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