title: Alkaline phosphodiesterase I of cultured mouse peritoneal macrophages. Distribution between cell surface and cytoplasm, turnover rate, and effects of colchicine.
abstract: Mouse peritoneal macrophages were cultivated in vitro and analyzed for activity of alkaline phosphodiesterase I. The specific enzyme activity was 2 to 3 times higher in thioglycollate-elicited than in resident cells and raised slowly for at least 3 days of culture in both cell types. Following phagocytosis of polystyrene latex beads the enzyme activity remained unchanged. About 90% of the activity was lost by treatment of the cells with the diazonium salt of sulfanilic acid (DASA) for 30 min at 37 degrees C. At 4 degrees C the corresponding degree of inactivation was only 40 to 50%. This temperature-dependent variation in the accessibility of the enzyme to inactivation by DASA could be related to the high rate of endocytosis in macrophages. During a 30 min incubation with DASA at 37 degrees C, large amounts of surface membrane will be internalized and replaced from the interior of the cell. Surface membrane is thus transferred into intracellular membrane and vice versa. Moreover, these membranes will be exposed to DASA independent of their location at the start of incubation. At 4 degrees C no comparable membrane traffic will take place. Treatment of the cells with cycloheximide at concentrations that inhibited protein synthesis by 90% or more left the enzyme activity essentially unaltered, indicating a slow turnover rate. On the basis of these findings, it is suggested that about half of the alkaline phosphodiesterase I activity of cultured macrophages is located in the plasma membrane. The other half is believed to be present in endocytic vesicles, lysosomes, and other as yet unidentified organelles that participate in the circulation of membrane constituents between the plasma membrane and the interior of the cell.
mesh_terms: D000818:Animals; D001202:Ascitic Fluid / Q000166:cytology; D002451:Cell Compartmentation / Q000187:drug effects; D002462:Cell Membrane / Q000201:enzymology; D003593:Cytoplasm / Q000201:enzymology; D004705:Endocytosis; D008264:Macrophages / Q000187:drug effects / Q000201:enzymology*; D051379:Mice; D010587:Phagocytosis; D043264:Phosphodiesterase I; D010726:Phosphodiesterase Inhibitors; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*
chemical_list: D010726:Phosphodiesterase Inhibitors; D010727:Phosphoric Diester Hydrolases; D043264:Phosphodiesterase I