Fig. 4. Subcellular fractionation of SV2 isoforms by sucrose gradient. A postnuclear supernatant of INS-1E cells was loaded on a sucrose density gradient (0.45-2 M sucrose) and centrifuged for 18 hours at 110,000 g. Aliquots of each fraction of the gradient were analyzed by western blotting using antibodies directed against carboxypeptidase H (CPH), synaptophysin (SVP38), SV2, SV2A, SV2B and SV2C. The top panel shows the amount of insulin present in the fractions corresponding to the distribution of insulin granules. Sucrose concentration was calculated from the refractive index of the fractions.