Purification and identification of secernin, a novel cytosolic protein that regulates exocytosis in mast cells.

After permeabilization with the pore-forming toxin streptolysin-O mast cells can be triggered to secrete by addition of both calcium and a GTP analogue. If stimulation is delayed after permeabilization, there is a progressive decrease in the extent of secretion upon stimulation, eventually leading to a complete loss of the secretory response. This loss of secretory response can be retarded by the addition of cytosol from other secretory tissues, demonstrating that the response is dependent on a number of cytosolic proteins.