Fig. 9. Discontinuous sucrose flotation gradients. MDCK cells transfected with either syn1A and munc-18-1 (a-e) or syn 1A alone (f) and untransfected Caco-2 cells (g) were lysed at 4°C in 1% (w/v) Triton X-100 and then loaded at the bottom of a discontinuous sucrose gradients. After centrifugation proteins in the collected fractions (1-8) and the pellets (P) were separated by SDS-PAGE, blotted onto a membrane and analyzed, using specific antibodies, for the distribution of transferrin receptor (TfR), munc-18-1 (M-18-1), actin, caveolin-1 (Cav), syn1A (Syn1) and syn3 (Syn3). Note that in the presence of munc-18-1 (+M-18-1), a portion of syn1A floats in a low density fraction, which also contains caveolin-1 and syn3.