Fig. 4. The majority of the trypsin-resistant SNAREs are not in SDS-resistant complexes. Chromaffin cells were permeabilised and exposed for 15 minutes to various [Ca²⁺], then maintained for a further 30 minutes in the absence (A) or presence (B) of 100 µg/ml trypsin, before being harvested in the presence of 2 mM PMSF and their membranes isolated. The samples were solubilised in SDS-PAGE sample buffer and split into two; one of each was boiled for 2 minutes. Boiled and non-boiled samples were subjected to SDS-PAGE and western blotting.