Evidence for the putative docking/fusion complex of exocytosis in parotid acinar cells

In lysates of the rat brain, the SNARE complex, a putative membrane fusion machinery of synaptic exocytosis, is extremely stable and is detected after SDS-PAGE. Applying this technique to parotid acinar cells, however, we could only detect the monomeric VAMP-2, but not the high molecular forms associated with other components of the SNARE complex. Parotid acini did not contain brain-type t-SNAREs, but contained NSF and alpha SNAP. When VAMP-2 was immunoprecipitated from parotid acinar cell lysates, NSF and alpha SNAP were coprecipitated with it. Since NSF and alpha SNAP are unable to bind directly to VAMP-2 but indirectly bind via t-SNAREs, the immunoprecipitate very likely contained unidentified t-SNAREs.