DISSOCIATION OF SNAP-25 AND VAMP-2 BY MGATP IN PERMEABILIZED ADRENAL CHROMAFFIN CELLS

in digitonin-permeabilized adrenal chromaffin cells, Ca2+-induced cate cholamine release can be resolved into at least two sequential steps: a MgATP-dependent priming step and a MgATP-independent Ca2+-triggered step. Botulinum neurotoxins types A and E cleaved SNAP-25, and blocked MgATP-independent Ca2+-induced catecholamine release from the permeab ilized chromaffin cells. When the permeabilized cells were primed by p retreatment with MgATP, the amount of SNAP-25 associated with VAMP-2 d ecreased, and the fraction of SNAP-25 proteolyzed by the neurotoxins i ncreased. These results suggest that dissociation of SNAP-25 and VAMP- 2 occurs during the MgATP-dependent priming step, and SNAP-25 plays so me important roles in the subsequent MgATP-independent step.