| Abstract: | Protein kinase activity of lymphocytes isolated from human subjects was assayed using histone as substrate. The activity was stimulated about twofold by cyclic AMP and total enzyme activity, determined in the presence of cyclic AMP, was inhibited by 65% by the specific heat-stable inhibitor of cyclic AMP-dependent protein kinase. Histone phosphorylation was not stimulated by cyclic GMP in the presence of the inhibitor. Cyclic AMP-dependent protein kinase could be activated in vitro by incubating intact cells with isoproterenol or with forskolin and was reflected by a significant (P less than 0.05) increase in the protein kinase activity ratio. In contrast to these well-characterized adenylate cyclase activators, incubating cells for up to 2 hr in vitro in the presence of the specific beta-blocker propranolol had no significant effect on the amount of cyclic AMP-dependent protein kinase that was in the activated state. When compared in subjects between the ages of 21 and 74 years, lymphocyte protein kinase activity was unaltered by age or gender. These results indicate that cyclic nucleotide-dependent protein kinase is of the cyclic AMP-dependent variety in the human lymphocyte. A low amount of the cyclic AMP-dependent activity (about 15%) is in the already activated state in freshly isolated cells, and this is not further reduced by incubation in vitro or by beta-blockade. In contrast to previously reported changes in the capacity to synthesize cyclic AMP, lymphocyte protein kinase is unaltered by gender or age in human subjects. |
