Lymphocyte Membrane Enzymes. II. Cyclic 3',5'-Adenosine Monophosphatase Located on Unstimulated Human Small Lymphocyte Nuclear Membranes

This study was undertaken to localize the enzyme cyclic 3',5'-adenosine monophosphatase in unstimulated human small lymphocytes. Cyclic AMP may be of importance in mediating lymphocyte stimulation, hence localization of the enzyme that is thought to modulate its intracellular concentration, cyclic AMPase, may point to the site of action of cyclic AMP in the cell. The histochemical technique employed was that of Shanta et al.⁶ Cyclic AMP substrate is degraded by the phosphodiesterase, then hydrolyzed, resulting in a lead phosphate precipitate at the site of enzyme action. This is subsequently visualized as lead sulfide. The enzyme was found to be localized on the nuclear membranes, which indicates that this is the site where cyclic AMP is destroyed. It does not necessarily mean that the nuclear membrane is the site where cyclic AMP is effective; this may be at some other point in the lymphocyte stimulation pathway, including the cell membrane, and the nuclear membrane may only be the site where cyclic AMP is degraded.